Astm stp 1453 2004

This system consists of silicone extrusions, tubes and joint protection collection reservoirs with one way valves JPCROV that are attached to the back of the concrete or stone panels usi

and Adhesives

Andreas T Wolf, Editor

ASTM Stock Number: STP1453

Printed in the U.S.A

Library of Congress Cataloging-in-Publication Data

Durability of building and construction sealants and adhesives / Andreas "1- Wolf, ed

p c m - (STP ; 1453)

Includes bibliographical references and index

ISBN 0-8031-3480-0

1 Building materials Testing Congresses 2 Sealing compounds Testing -Congresses

3 Sealing compounds Deterioration Congresses 4 Adhesives Testing Congresses 5 Adhesives Deterioration Congresses I Wolf, A.T (Andreas"1".) I1 Series: ASTM

special technical publication ; 1453

Peer Review Policy

Each paper published in this volume was evaluated by two peer reviewers and at least one edi- tor The authors addressed all of the reviewers' comments to the satisfaction of both the technical editor(s) and the ASTM International Committee on Publications

To make technical information available as quickly as possible, the peer-reviewed papers in this publication were prepared "camera-reedy" as submitted by the authors

The quality of the papers in this publication reflects not only the obvious efforts of the authors and the technical editor(s), but also the work of the peer reviewers In keeping with long-standing publication practices, ASTM International ~ a i n s the anonymity of the peer reviewers The ASTM International Committee on Publications acknowledges with appreciation their dedication and con- tribution of time and effort on behalf of ASTM International

Printed in Bridgeport, NJ

2004

Structural Glazing Failure Five Case Studies M E BAKER 37

Quality Control Guidelines for Factory Applied Structural Silicone G l a z i n g - -

Historical Development and Future Prospects of Structural Silicone Sealants

in China Y.-L W A N G , H - M W A N G , A N D L - M W U 56

F A C T O R S I N F L U E N C I N G T H E D U R A B I L I T Y O F S E A L E D J O I N T S A N D A D H E S I V E F I X A T I O N S

Influence of Polyester Powder Coating Chemistry on Adhesion Dire'ability of

Water Absorption in Cold Liquid-Applied Waterproofing J c STRONG AND

Estimation o f the Fatigue Resistance of Sealants to Movement at Intersections

of Sealed Joints and Improvements in the Joint Design M e t h o d - -

Effect of Float Glass Surface Composition on Silicone Sealant Adhesion Tested After Simultaneous Exposure to Hot Water and Ultraviolet L i g h t - -

A T W O L F , C S M c M I L L A N , W STIELL, AND K LIEB 252

Comparison of Butyl versus Modified Asphalt Window Flashing Adbesives

A D Z1MA, J R , T A W E S T O N , J D K A T S A R O S , AND R H A G O O D 262

Durability o f H o r i z o n t a l S e a l a n t Joints D H N / C A S T R O A N D V D G O R M A N 2 8 0

Durability and Adhesion Rate of One-Part Silicone Sealants to Silicone

Rubber Extrusions for New and Remedial Glazing and

Sealant Failure Morphology The Important Criterion of Equipment

Selection for Weathering Studies G WYPVCH, s KUBERSKI, AND F LEE 310

Developing a Performance-Based Joint Sealant Specification for Airport PCC

Harmonization and Optimization of Weathering Test Methods for Building

FIELD EXPERIENCE WITH SEALED JOINTS

AND ADHESIVE FIXATIONS

problen~ The damages attributed to water and air infiltration can be corrosion of structural anchors, reduction in insulation efficiency, damage to interior walls, damage to floor coverings and mold growth This paper reports on the design, development and testing o f a state of the art secondary drainage system that is used behind prefabricated panelized Glass Fiber Reinforced Concrete (GFRC), Architectural Precast Concrete (APC), Composite Architectural Precast (CAP), and natural stone on truss systems This system consists of silicone extrusions, tubes and joint protection collection reservoirs with one way valves (JPCROV) that are attached to the back of the concrete or stone panels using adhesive attachments, which are compatible and marry intimately into the exterior architectural sealant joints Unique designs of gutters that are resistant to jobsite debris that can clog drains and render them inadequate are presented along with the JPCROV that prevents percolation and allows water to weep out

of the system- These additional materials within the wall cavity also must have benign fire properties due

to the concern for toxic gasses and smoke in the event of a fire

The technology of the silicone extruded gutters, tubes and percolation boxes is most suitable for the alkaline variable temperature and humidity environment found in these wall cavities Silicone adhesive technology of one-part neutral cure RTV silicone sealant is used to mount the secondary drainage system within the wall to provide a long-term performing solution Durability data is presented on the bonds between the silicone extrusions and concrete substrates for this application Modified ASTM Standard Test Method for Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to-Metal) (D1002-99) data aider room temperature cure, water immersion, and both elevated temperature and high humidity is presented as data simulating the actual application System design capacities and proper installation for maximum coverage are also presented

KEYWORDS: exterior cladding, infiltration, drainage system, silicone extrusion, durability, ASTM D1002

I n t r o d u c t i o n

M o d e m m i d - to high-rise buildings are p r e d o m i n a t e l y c o m p r i s e d o f a structural steel or cast

in place concrete f r a m i n g s y s t e m u p o n w h i c h all other building elements are supported Walls,

1 Associate Industry Scientist, Dow Coming Corporation, P.O Box 994, Midland, MI 48686-0994, U.S.A

2 Chief Estimator, Clark Pacific, 1900 South River Rd., West Sacramento, CA 95691-2888, U.S.A

3

4 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

floors, electrical, plumbing and HVAC systems all attach to this structure The exterior of the support structure is typically clad with and supports the above-mentioned panelized systems as well as glass/curtainwall systems, metal panels, stucco, Exterior Insulation Finish Systems (EIFS) or plaster These cladding systems must be made to pass specifications regarding air and water infiltration Specifications have been created to minimize air and water infiltration so that buildings can operate the heating and cooling systems efficiently and remain structurally sound over the life of the building

These panelized barrier systems typically have joints between each individual panel that require a high performance sealant, a sealant that has greater than +25% joint movement ability per ASTM Standard Test Method for Adhesion and Cohesion of Elastomeric Joint Sealants Under Cyclic Movement (Hockman Cycle) (C719-93 (1998)) The purpose of the high performance sealants is to provide air and water tight panel joints on the exterior face of the panel systems These sealants are required to have elastomeric properties to accommodate joint movements created by thermal expansion and contraction, interstory building drift due to wind or seismic movements, elastic frame shortening and creep An elastomeric material is also referred

to as a material that has elastic recovery or memory Elastomeric silicone sealants are commonly used in commercial buildings to protect wall systems from water intrusion The sealant is installed over a back up or bond tape The backer rod supports the sealant until it has cured and is typically made of polyurethane or polyethylene foam The intended use of the backer material is

to provide a proper joint shape that allows the sealant to expand and contract as required Once the sealant has cured, in conjunction with the exterior cladding, it forms the primary waterproofing barrier system for the building The main suppliers of silicone sealants typically have excellent quality control and testing procedures and utilize applicators or caulking subcontractors, trained in the use of the products Silicone sealants have proven to be very effective when the bond line is properly detailed and the edges of the panels are cleaned and prepared allowing the sealant to develop durable adhesion to the panel substrate Silicone sealants have proven to be excellent long lasting sealing materials well suited for providing the weatherproofing protection in barrier wall systems

The primary exterior sealant system can fail or be compromised in many ways allowing a building to leak Sealant installation is highly dependent on skilled workmanship Improperly detailed joints that do not allow for proper sealant installation and poor workmanship can combine, creating adhesive or cohesive failures of the sealant Joint failures can also occur when exterior panelized systems are damaged, allowing water to bypass the sealant at the joints Failures can also occur at the interface with glass and curtain wall systems This interface can lead to compatibility and workmanship problems associated with the coordination of tradesmen working on the project The proper sealant best used for architectural precast concrete joints may not be the proper sealant for an architectural precast concrete panel abutting an aluminum window mullion These interfaces and improperly installed caulk joints may lead to potential water penetration inside the building Joint failures from building movements due to wind- induced interstory drift or seismic events can occur Sealants can degrade over time from exposure to the elements and repeated cyclic thermal expansion and contraction Therefore, they will require replacement during the life of the building

When leaks occur, the damage caused to the building can be further amplified due to percolation Percolation occurs when sustained high winds or a positive external pressure due to the HVAC system can vacuum water through the damaged sealant joints or cladding The water

that is attached to the interior surface of the exterior panels that backs up the primary waterproofing system This solution has come about due to numerous sealant failures, the use of inexpensive less durable cladding systems, and/or poor quality panelized systems that have resulted in the damaged parties seeking redress in high profile lawsuits These situations have resulted in architects and exterior wall consultants mandating that a secondary drainage system

be used in addition to the primary system (e.g the sealant caulk joint) to prevent water damage

to buildings

This paper is written to discuss a secondary drainage system that is installed as a back up to barrier wall construction utilizing precast concrete, GFRC, and natural stone on truss panel systems used in commercial construction The system consists of extruded silicone rubber gutters, and molded parts that are part of an engineered system that allows water to be effectively routed out of a wall system if the primary barrier wall is breached The extruded silicone gutters are attached with Room Temperature Vulcanizing (RTV) neutral cure silicone sealants to the backside of precast concrete, GFRC, or natural stone and must withstand the spandrel environment for years The RTV silicone sealant is also used to attach the silicone gutters, tubes, splices and valves together The drainage system can be placed onto concrete panels that may reach 9 m (30 feet) in width

The question of durability is brought about as the RTV neutral silicone adhesive sealant is required to form a permanent bond to the backside of preeast concrete, GFRC and natural stone The backsides of these panels are not visible from the exterior of the building Hence, there is little attention paid to these surfaces Will the panel supplier be able to provide a surface suitable

to apply sealants, free of loose dust, laitance, dirt, and grease? How can this be done? Will the adhesive be able to hold up in a spandrel environment with the thermal and humidity cycling that

is present?

This paper intends to address these questions using a testing methodology on real surfaces that has been put together in a logical fashion

Performance Requirements of the Gutter System

The secondary drainage system is a system of horizontal gutters applied on the backside of spandrel panels to collect any condensation and water that collects and falls down the back of the panels The system has a slope built into it that allows collected condensation and rainwater to

6 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

drain out through engineered valve boxes placed in the exterior vertical sealant joints, see Figure

FIG l - - C u t away section o f the gutter system installed on a precast concrete panel (System consists o f gutters attached to the backside that drain water to valve boxes mounted in the

vertical joints)

The gutter as designed has a mass o f 0.5 grams per millimeter (0.34 lbs per foot) o f length

If the gutter were to be full o f water, the gutter would weigh 1.0 gram per millimeter (0.68 lbs per foot) o f length Hence the adhesive should be designed to support the weight o f the gutter full o f water without having any negative impact on the bond

The gutter system must be capable o f removing the water resulting from leaks and condensation that can breach the primary system The largest concrete panels that this could be used with measure 9 m x 3 m (30 ft x 10 fl)

Silicone RTV sealants have not been used to attach items to concrete-based materials in the past However, it is common in a sealant-testing laboratory to attach concrete blocks to aluminum supports that rest inside an accelerated weathering machine Personal experience by one of the authors is documented in A S T M STP 1200 [1] This author had 63 tensile adhesion joints made of concrete to concrete, each weighing about 250 grams (0.55 lbs), attached to aluminum with about 1250 turn 2 (2 in 2) RTV neutral cure silicone sealant O f the 63 samples, 21 were exposed to 1000 hours, 21 were exposed to 2500 hours, and 21 were exposed to 4000 hours

of QU-V 3 accelerated aging The adhesive sealant never saw the UV light, however it did see

3 QUV Weathering Tester Q-Panel Lab Products, 800 Canterbury Rd, Cleveland, OH 44145, USA

Experimental Method

Silicone is generally thought to bond well to silicone extrusions This has been documented

in ASTM STP 1441 [2] Based on past testing, acceptable bonds to extruded silicone rubber are reliable and durable The focus in this study is to determine the durability of the silicone RTV adhesive sealants on the concrete

The extruded gutter made of heat-cured silicone rubber has a Durometer of 80 Shore A, tensile strength of 8.3 MPa (1200 psi) at 135% elongation per ASTM Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers Tension (D412-98a(2002)el), and a tear strength of 14.1 N/ram (80 pounds per inch) per ASTM Standard Test Method for Tear Strength

of Conventional Vulcanized Rubber and Thermoplastic Elastomers (D624-00)

Samples of the extruded silicone rubber gutter were cut into 25 x 25 mm 2 squares and attached to the backside of GFRC panels cut into 25 x 25 x 75mm 3 pieces Test specimens can be seen below in Figure 2,

FIG 2 Square pieces o f rubber (25ram x 25 mm) and pieces of GFRC (25ram x 25ram x 75mm)

8 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

A dollop or small spherical bead of RTV adhesive sealant was then placed on the concrete and the rubber pressed into it The rubber was pushed down till the adhesive had a thickness between 0.5-1mm (see Figure 3)

FIG 3 Rubber attached to the backside o f GFRC with dollops o f RTV silicone pressed down to

0.5-1mm thickness

After the silicone RTV had 14 days to cure, a piece of aluminum was attached to the rubber with a high strength RTV silicone adhesive so that the rubber could be pulled off in shear from the concrete surface The high strength silicone RTV adhesive was chosen to have strength substantially higher than the concrete bonding adhesives used in the study This way a reasonable model for concrete bonding strength could be obtained The aluminum was pulled in shear from the GFRC backsides at a rate of 12.5 mm per minute Hence this method of testing is closest to the testing specified in ASTM D1002

GFRC was chosen as the substrate as this was believed to be the worst-case scenario The surface is extremely rough and variable This rough surface is what the drainage system must be attached to in the field ASTM standard concrete for sealant testing was not chosen because this substrate is not typical in the field with the nice uniform cut or cast surfaces

Two silicone RTV adhesive sealants (three conditions) were evaluated in this study

1 Sealant A, no primer on concrete or rubber Medium modulus RTV, alkoxy cure, meets ASTM Standard Specification for Elastomeric Joint Sealants (C920-02), Type S, Grade NS, Class 50, Use NT, G, A, and O Stress at 25% strain of 0.28 MPa (40 psi) per ASTM Standard Test Method for Determining Tensile Adhesion Properties of Structural Sealants (C1135-00)

2 Sealant A with primer on concrete, no primer on rubber An epoxy barrier primer was applied to the concrete

3 Sealant B, no primer on concrete or rubber, low modulus RTV, amide cure, meets ASTM C920, Type S, Grade NS, Class +100/-50, Use T, NT, G, A, M, and O Stress at 25% strain of0.11 MPa (15 psi) per ASTM C1135

appropriate to simulate the high heat and humidity found in a spandrel cavity on a typical jobsite using the 2500 hours of elevated heat and humidity This heat cycle was determined based on intuition, experience, and the availability of test equipment

Discussion of Results

Six specimen conditions are reported after four exposure conditions

1 Sealant A, no primer on brushed concrete

2 Sealant A, no primer on sandblasted concrete

3 Sealant A with primer on brushed concrete

4 Sealant A with primer on sandblasted concrete

5 Sealant B, no primer on brushed concrete

6 Sealant B, no primer on sandblasted concrete

The four exposure conditions are room temperature cure, one-day water immersion, seven days water immersion and 2500 hours at 50~ and 90%RH

The samples were pulled apart in shear at a pull rate of 12.5 ram/minute Strength is reported

in MPa and in psi Triplicate samples were made and all data are reported This is done because the thickness of the adhesive is variable due to the natural condition of the backside of the GFRC tested Hence, the scatter in the data is as important as the average strength Results are presented below in Table 1 and in Figure 4

The data show that sandblasting the backside of the GFRC substrates gave better strength and less variability at the room temperature cure but was inconclusive after the water immersion and after 2500 hours of 50~ and 90%RH

Sealant A had increased strength and less variability when the epoxy primer was used on the GFRC panels This was not a surprise because this product used in the field requires primer to gain acceptable adhesion to concrete The epoxy barrier primer showed superior results comparedto no primer This is due to the shielding of the alkalinity in the eonerete from the silicone bond The accelerated aging at 50~ and 90%RH clearly shows the effects of the alkalinity on the silicone bond in the thin sections Past testing in the QUV on concrete has not shown this type of strength loss [1], however that testing was according to ASTM C1135 as opposed to this modified ASTM D1002 procedure

10 BUILDING/GONSTRUCTION SEALANTS AND ADHESIVES

Sealant B is an excellent low modulus weatherproofing sealant used o n concrete without primer Sealant B showed lower strength on the test specimens, because it has lower tensile strength compared to Sealant A as measured both b y A S T M D412 and A S T M C1135 Sealant B showed less variability during the testing compared to unprimed Sealant A because o f its better adhesion characteristics to concrete after room temperature and water immersion, however the results were poor after the accelerated aging Again this result is due to the alkalinity in the concrete and the configuration o f this test The epoxy barrier primer was not used in conjunction with this material because o f a chemical incompatibility between the two

T A B L E 1 - - Shear strength of RTV adhesives

Sealant Shear strength after conditioning, in MPa and in (psi)

21 days RT 1 day water 7 days 2500 hrs 50~

Sealant A, no primer, on brushed 0.21 (29) 0.64 (91) 0.14 (20) 0.099(14)

0.61 (86) 0.62 (88) 0.51 (72) 0.014 (2) 0.31 (44) 0.54 (76) 0.24 (34) 0.047 (7) Average

Sealant A, no primer on sandblasted 0.40 (57) 0.60 (84) 0.20 (28) 0.043 (6)

be practically achieved with real surfaces and real application methods It is suggested that Sealant A with the barrier primer is the appropriate adhesive combination to adhere the gutters to the backside o f the concrete panels that will b e exposed to heat and humidity present in the spandrel sections o f typical commercial buildings All data show ultimate strength values above

FIG 4~Average shear strength data of sealant, primer and surface preparation conditions at

four conditions

Practical Applications and Summary

The gutters for this secondary drainage system are attached in the field by field mechanics skilled in the tasks o f cleaning surfaces and applying RTV sealants Precast concrete, GFRC or natural stone on truss systems that can use a secondary drainage system can have the backside surfaces sandblasted before the panels are transported to the jobsite This is practical

Using the above data, how much sealant is practically required to attach the gutters to the backsides o f the panel systems?

The silicone RTV adhesive sealants have a low initial strength and actually behave more as a lubricant when they are wet and first installed The gutters typically require an adhesive system that will hold the extrusions to the backside o f the panel while the silicone adhesive sealant CUTCS

The gutter shown in Figure 5 is 37 mm tall Using an extruded bead o f silicone RTV adhesive sealant 6-9 m m (0.25-0.375 inches) in diameter adjacent to an adhesive tape 1.0 rnm in thickness, and placing the gutter onto the concrete, will result in an adhesive bead o f 1 m m x 12 ram along the entire length o f the gutter

12 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

Instructing field mechanics to clean a gutter and apply a 6-9 mm diameter sealant bead to the backside o f the gutter is a practical application

FIG 5 Gutter system using a mastic adhesive tape for temporary support while the silicone

adhesive sealant cures

The resultant stresses placed upon the adhesive sealant by gravity can be easily calculated i f

we consider that 12 m m o f continuous contact is achieved on the gutter to panel interface The gutter as designed and shown in Figure 5 has a weight o f 500 grams per meter empty or

1000 grams per meter i f it were full o f water (0.34 pounds per foot empty and 0.68 pounds per foot if it were full o f water) I f the adhesive achieves 12 mm (1/2 inch) o f continuous contact with the gutter, the resultant stress on the adhesive would be 0.4 kPa empty or 0.8 kPa full (0.057 psi empty or 0.11 psi full) These numbers are three orders o f magnitude less than the test data presented above

Although both Sealant A and Sealant B can be used to support a gutter system using the system described above, Sealant A used in combination with the barrier primer on sandblasted concrete is suggested because o f the retention o f strength after dry, wet and 2500 hrs at 50~ and 90%RH As the gutters are attached to individual panels, live building movements are not transferred to the adhesive beads The adhesive will need only to support the weight o f the gutter The induced gravity forces involved are minor and there are no live building forces or movements placed upon the gutter system once the construction is finished

Acknowledgment

The authors would like to thank B J Raab, John W Smith and Michael R Bott for coordinating the testing and evaluation of data for this study Without their work and engineering, this data could not have been taken Coordination o f the special testing apparatus to test the specimens in shear is much appreciated

Mark K Schmidt'

Lock-Strip Gasket System Retrofit: A Case History

REFERENCE: Schmidt, M K., "Lock-Strip Gasket System Retrofit: A Case History," Durability

of Building and Construction Sealants and Adhesives, ASTM STP 1453, A T Wolf, Ed., ASTM International, West Conshohocken, PA, 2004

ABSTRACT: The facade of the subject 20-year-old, three-story building is comprised of insulating

glass units in vision areas and single monolithic glass sheets in spandrel areas Both products have a reflective metallic coating on the exterior surface and are completely captured by a perimeter lock-strip (zipper) gasket system The zipper gasket intersections are butted, not vulcanized, causing numerous Oavenues for water penetration Attempts to seal some of these gaps with sealant had been made in the past, yet active leaks still existed Furthermore, there was a concern regarding the premature failure of the insulating glass units within the inadequately drained glazing pockets of the zipper gasket system

In order to address these gasket conditions properly and to protect the insulating glass units for the long-term, custom designed repairs consisting of overlapping preformed silicone shapes and extrusions were utilized to create a watertight barrier Unique elements of this application include accommodation

of undulating gaskets and misalignment of intersecting gaskets, complete coverage of the previously repaired lock-strip gaskets (believed to be contributing to the glass staining) with the preformed shapes and extrusions, sealant pockets within the extrusion to control bond surface area, and selection of sealant adhesive to mitigate future glass staining Lessons leamed from the application of this barrier system, including issues related to sizing and fabrication of the preformed silicone parts, are presented The experiences gained via the prolific use ofpreformed silicone products on this project will be beneficial to all those involved in the maintenance of lock-strip gasket systems and other types of building facades

KEYWORDS: preformed silicone, zipper gaskets, lock-strip gaskets, silicone adhesive, sizing articles

Background

In late 1999 as part of a larger prepurchase assessment, the facade of a three-story office building in the western United States was inspected for signs of existing or imminent problems The facade consists of a lock-strip (zipper) gasket system with vision insulating glass units and spandrel glass sheets The insulating glass units consist of two 6

mm thick glass sheets separated by a 13 mm wide metal spacer The spandrel glass is a

contains approximately 820 insulating glass units and 1 080 spandrel glass sheets No shop drawings or architectural drawings of the curtain wall were available for review

the early 1990s, a number of failed insulating glass units were replaced As a result, concerns were raised on behalf of the prospective buyer regarding the current condition and hture performance of the insulating glass units Subsequent frost point testing at

' Consultant, Wiss, Janney, Elstner Associates, Inc., 330 Pfingsten Road, Northbrook, IL, 60062

FIG 1 - Gaps (arrows) at Intersections of Lock-Strip Gaskets

At the sill of some insulating glass units, the glass-to-gasket joints had been wet sealed with an early generation silicone sealant Glass staining was prevalent at these locations (Figure 2), as well as areas adjacent to concrete sidewalks and irrigation sprinkler heads

FIG 2 - Staining of Glass Adjacent to Early Generation Silicone Sealant

In an attempt to provide drainage in the glazing pocket, retrofitted weep holes had been installed in the zipper gaskets along the sill of the insulating glass units These boles were frequently obstructed by burrs and were located between setting blocks, about

3 mm above the bottom of the glazing pocket These weep holes did not adequately drain

16 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

the glazing pocket between the setting blocks, nor did they aid in draining the area between the setting blocks and the ends of the glazing pocket

There were localized depressions in the zipper gaskets at the setting block locations below the insulating glass units (Figure 3) The setting blocks were found to be shorter than required, but installation o f longer setting blocks would probably not eliminate the set undulations in the gaskets Evidence ofponding water in the form o f stains on the spandrel glass was evident at the existing depressions (Figure 3) Ponding water in the glazing pocket could cause premature failure of the insulating glass units

FIG 3 - Localized Depressions (arrows) in Zipper Gaskets and Weep Holes

Due to the historically poor performance of insulating glass units in lock-strip gasket systems, an appreciable future service life for the units could only be assumed if repairs were made to the lock-strip gaskets To address the gasket conditions properly and to

protect the insulating glass units for the long term, repairs for transforming the lock-strip gasket system into a watertight barrier were designed and implemented

Repair Design

In the repair design phase, several different repair schemes were considered, including one published as a project profile by a major sealant manufacturer [1] and an engineering investigator [2] Historically, schemes for sealing lock-strip gasket systems have utilized a combination o f wet seals between the neoprene gaskets and the glass and wet sealant overlays or preformed silicone tape to seal the gasket intersections As an additional step to reducing potential water penetration, some historical repair schemes have also included removal o f the lock-strip (the center spline that creates pressure between the gasket and the glass), application of sealant in the lock-strip cavity, and replacement o f the lock-strip

Trial applications o f two recognized schemes were installed on the subject building (Figure 4) Each application included a silicone wet seal around the glass perimeter with either a silicone sealant overlay or preformed silicone tape over the gasket intersections Neither application included any treatment of the lock-strip itself, because successful removal and replacement o f the relatively tight lock-strips seemed dubious at best

FIG 4 - Trial Repairs Utilizing Silicone Wet Seals and Localized Sealant Overlays or

Preformed Silicone Tape

In order to address the potential avenues for water penetration through the lock-strips, another trial application was installed that involved the use of overlapping preformed silicone tape (Figure 5) All of the trial applications relied heavily on the bond between the perimeter silicone wet seal and the weathered neoprene gaskets At gasket

intersection locations, three-sided sealant adhesion conditions and limited bond between the silicone wet seal and the integral sealant overlay or preformed silicone tape raised concerns regarding the longevity of the trial repairs Furthermore, none of these trial applications enhanced the aesthetics of the facade, particularly the unsightly depressions

18 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

the appearance of the facade The design incorporated hat-shaped silicone extrusions that completely covered the existing gaskets Using integral flanges, these extrusions could

be adhered to the glass without relying on bond to the weathered and previously wet sealed neoprene gaskets Proper sizing and installation of the extrusions during the construction phase would also effectively conceal the depressions in the existing gaskets and misaligrmaents of intersecting gaskets Ultimately, the final design utilized silicone extrusions placed over the existing gaskets with shingle-laps at intersections (Figure 6) and molded silicone shapes installed over the lapped extrusions at gasket intersections (Figure 6)

FIG 6 -Final Repair Design Utilizing Lapped Preformed Silicone Extrusions (left) and

Molded Silicone Shapes over Lapped Extrusions (right.)

Testing and Fitting of First Articles

The original extrusion design included a wall thickness of approximately 1.5 ram Due to warping concerns during curing o f the extrusions, the fabricator recommended increasing the wall thickness o f the first article silicone extrusions to approximately 2.1 nun At the recommendation o f the installation contractor, sealant pockets were formed in the flanges of the hat-shaped extrusion to control bond surface area In lieu of the traditional silicone sealant/adhesive recommended by the manufacturer, an alternate adhesive with less fluid (and plastieizers) was selected to minimize the potential for staining o f the sensitive exterior reflective coating o f the glass Shore A durometer hardness of 50 + 5 points per ASTM Test Method for Indentation Hardness of

Elastomeric-Type Sealants by Means of a Duronaeter (C 661) was also selected for the extrusions and molded shapes

In addition to the standard adhesion tests [3] performed by the sealant manufacturer prior to implementation o f the repairs, sizing and fitting of first article extrusions and shapes was performed in conjunction with the installation contractor Based on dry-fit sizing and limited installation of the hat-shaped extrusion and selected shapes, the first articles were determined to be undersized The tight fit over the existing gaskets caused the extrusions to cup and the flanges to pull away fi-om the glass (Figure 7) Nonuniform contact o f the flanges with the glass created installation difficulties The silicone shape

FIG 7 - First Articles: Cupped Extrusion (left) and Cupped Four-Way Intersection with

Pinhole (arrow, righO

Larger second article silicone parts were ordered after the initial sizing The fit of the second article extrusions (Figure 8) appeared to be optimal with regard to maintaining its shape, eoneealing the depressions in the existing gaskets, and minimizing the reduction in the daylight opening The preformed silicone shapes were also adequately sized to accommodate misalignments between opposing tiorizontal gaskets at gasket intersections (Figure 9)

FIG 8 - Proper Fit of Second Article Extrusion and

Integral Sealant Pocket (arrow)

2 0 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

FIG 9 -Misalignment in Opposing Covered Horizontal Gaskets (arrow, left) and

Adequate Accommodation at Four-Way Intersection (right)

FIG 1 0 - Wood Template for Masking (left), Application of Adhesive (center), and

Setting Extrusion in Sealant (right)

While moderate winds typically do not hamper a conventional wet sealant project, they do pose a significant challenge to tradesmen handling nearly 2 m long sections of

FIG 11 - Undulating Sight Line of Horizontal Extrmions (arrow, left) and Improved

Sight Line of Horizontal Extrusions (arrow, right)

The repair specifications assigned the responsibility for field adhesion testing to the sealant manufacturer Based on the sealant manufacturer's warranty requirements, field adhesion tests [3] were performed on a random basis at a minimum of one per elevation,

on each floor of the building, on each substrate/sealant product combination No

unacceptable test results were reported by the sealant manufacturer

Two fabrication problems were experienced during the course of this project: warped and bowed extrusions Although the original extrusion wall thickness was increased to 2.1 mm, some extrusion lots were delivered to the site with warped flanges that precluded proper installation Other lots of extrusions exhibited an overall bow that made proper installation cumbersome All problematic lots were returned to the fabricator for

replacement extrusions No explanation for either occurrence was offered by the

fabricator, although it is surmised that difficulties were experienced in the curing phase of fabrication

Overall the custom repair scheme implemented on this structure (Figure 12) met the design criteria of mitigating all potential avenues for water penetration while enhancing the appearance of the facade

2 2 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

FIG 12 - Representative Area of Completed Repairs

Summary of Lessons Learned

This case history of repairs to a loek-slrip gasket system has included issues related to repair design development, testing and sizing of preformed silicone parts, and

implementation issues The lessons gleaned from this case history are summarized below

9 Complete overcladding of the gaskets with overlapping preformed silicone extrusions and molded shapes is an effective way of creating a weatherproof barrier system while at the same time enhancing the appearance of the facade

9 The implemented repair scheme consisting of preformed silicone extrusions and molded shapes does not rely on the bond of wet silicone sealant to weathered neoprene gaskets or residual sealant from previous repair attempts

9 Proper sizing and installation of the extrusions and shapes can conceal

depressions, misalignments, and other imperfections of existing gaskets

9 In the construction phase, sufficient lead time for sizing and revising first articles should be allowed On this project, fabricating the first and second articles, as well as the final production run, each required approximately six to eight weeks The design/construction/fabrication team should consider methods to minimize the number of articles and streamline the fabrication process

9 Longer length extrusions will likely require segmental installation in order to provide temporary gravity and lateral support during moderate winds

9 Extrusions should be restrained from significant movement during tooling operations to maintain straight sight lines

9 Close coordination with the preformed silicone fabricator may alleviate some warping/bowing problems associated with delivered extrusions

References

[ 1 ] Dow Coming, "The Consultant's Update - Repairing Weathered Zipper Gaskets,"

Consultant's Guide to Silicone Building System, Waterproofing & Restoration Products,

Midland, MI, March 1997

Anneliese H a g l 1

Journal of ASTM International, March 2004, Vol 1, No 3

Paper ID JAIl1601 Available online at www.astrn.org

Durability by Design: Load Carrying Silicone Bonding, Herz Jesu Church, Munich

ABSTRACT: The design of conventional glass facades in Germany is typically based on the extensive use of point supports that keep the glass panels in position and which provide the load transfer of the fagade Besides the aesthetic disadvantage of discrete elements being visible in the glass fa9ade, the application of point supports leads to highly concentrated stress regions substantially affecting sizing and durability of the fagade components In order to overcome these limitations, a new approach has been chosen for the design of the glass fagade of the Herz Jesu Church, Munich One peculiarity of the overall glass fagade of this box-shaped building consists in horizontal and vertical glass beams used for the support of the fagade Silicone adhesives bond steel stringers along the main edges of the horizontal and vertical glass beams in order to establish load paths between beams and fagade The hereby-realized bonding design offers special features being favorable for the durability of the building Load carrying capacities have been provided by line-type connections, substantially reducing stress concentxations Major attention has been given to the geometric layout of the bonding Thus, detailed finite element (FE) analysis has guided the careful selection of an adequate channel cross section for the stringers The design philosophy of the bonding is characterized by a small exposed surface of the silicone adhesive, offering only a very small area of attack for environmental degradation Additionally, the exposed surface is only stressed at a low level avoiding the critical combination of highly loaded areas exposed to aggressive environmental conditions Furthermore, two principal load paths (tension and shear) are established, leading to a fail-safe design principle of the bonding These key considerations provide major contributions to the high durability design of the glass fagade bonding

KEYWORDS: structural glazing, durability design, joint geometry, FE analysis

i Managing Director, A Hagl Ingenieurgesellsehafl mbH Munich, Pasinger Str 16, 82166 Graefelfing, Germany

Copyright 9 2004 by ASTM Intematiorml, 100 Barr Harbor Ddve, PO Box C700, West Conshohockcn, PA 194,28-2959

FIG 1 - - Glass facade o f Herz Jesu Church, Munich

The innovative application of glass in the fagade serves to emphasize the fundamental idea of the architecture using the style of a rock crystal On the other hand, the glass skin plays a major role in the arrangement of the inside illumination by defined transparency gradation of the glass fagade elements Therefore, the architects asked for a glass facade with a minimum of visible load-carrying structures In order to meet these requirements, two sophisticated technologies have been applied [ 1 ] First, horizontally and vertically arranged glass beams serve as supporting members for the glass fagade Second, the conventional approach extensively using point supports was abandoned in favor of load-carrying line-type bonding using silicone adhesives As the functionality of these technologies guarantees the integrity of the glass fagade, special emphasis was given to strength and durability of these structural elements during the design of the fagade by experimental and theoretical studies After giving a short overview concerning the peculiarities of the fagade design affecting the requirements for the bonding, this paper presents design aspects, including Finite Element Analysis results of the bonding geometry, considered in order to assure adequate durability behavior of the glass facade

26 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

Design of the Faqade of the Herz Jesu Church

The skeleton of the glass facade consists of a steel framework stretching out the box shape of the building with the dimensions 47.04 m (length), 19.00 m (width) and 16.00 m (height) The steel framework is based on constant raster units of 6.72 m in longitudinal axis and 6.39 m in lateral axis In the vertical direction, the raster units increase from the top to the base by an arithmetic series from 1.56 m to 2.40 m for architectural reasons The primary load-bearing members of the steel framework are eight rigid steel frames arranged in longitudinal direction according to the raster units (Fig 2)

19,00 m ~

Honzon~l Bracings

Longitudinal Bracings Longitudinal Beam between Frames FIG 2 - - Structural sSystem of Herz Jesu Church, Munich

In order to achieve minimum cross sections for aesthetic reasons, the steel frames are composed of two welded hollow sections Furthermore, the shifting of the steel frames towards the inside of the building enhances the impression of a facade almost exclusively consisting of glass Bracings mounted on the top and on the longitudinal sides strut the structure and establish the load path for wind and other loads in the longitudinal direction of the building The bracings are elastically tailored in order to achieve similar deformations in lateral directions for minimum interlocking within the glass fagade

In order to realize an unobtrusive load-beating structure, the design concept of a hanging fixation system has been selected for the glass facade This system allows to achieve slender frame elements by avoiding destabilizing compression loads The glass facade consists of the following major components (Fig 3):

9 Insulating glass units (width 3.35 m) as core components of the glass fagade; two elements are grouped within one raster unit;

9 Horizontal glass beams (length 6.70 m) connecting facade and suspender bars with the steel frames;

FIG 3 - - Detail of the hangingfixation system of the glass facade

9 Horizontally arranged fagade stringers for the transfer of wind loads from the insulating glass units to the horizontal glass beams

In order to achieve the load-bearing connection of the horizontal and vertical glass beams to the suspender bars, the beams are bonded by a silicone-based conventional structural glazing adhesive (DOW CORNING | DC-9932) to steel stringers The steel stringers are provided with discrete attachment points for connection by bolts to the facade stringers and suspender bars in order to allow easy assembly and maintenance

The horizontal glass beams have the primary function to transfer wind pressure and wind suction loads acting on the glass facade to the steel frames In order to establish the load path between glass facade and steel flames, each sla'inger bonded to a horizontal glass beam has eight attachment points for connection to the horizontal facade stringers (Fig 4) Concerning the certification of the bonding, the wind suction case is considered as critical load case because the bonding has to withstand tension forces The wind suction load case is characterized by high peak forces (approximately 1.6 kN for the critical bolt connection) acting on the bonding during short periods

2 Dow Coming S.A., Pare Industriel, 7180 Seneffe, Belgium

2 8 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

FIG 4 - - Stress distribution of conventional structural joint (one-sided bonding)

The vertical glass beams support the horizontal glass beams in order to ensure the integrity of the structure of the glass fagade The vertical glass beams act as mounting brackets using two attachment points of the bonded stringers for connection to the suspender bars (Fig 5) In order

to generate a reacting moment for the offset of dead loads, a force couple (approximately 0.3 kN) acts on the two attachment points, one being loaded by compression, the other (critical) one by tension This dead load case is characterized by time invariant loads (approximately 1.8 kN in vertical direction and 0.3 kN in horizontal direction for the critical bolt connection); the shorter glass beams showing larger stress levels in the bonding due to the shortened lever ann

Bonding Technology for High Durability

According to Kinloch [2], observations have shown that the following parameters substantially affect joint durability

9 Environment: Moisture has been identified to be the most aggressive environmental factor for structural adhesive joints, leading to significantly decreased mechanical performance

9 Temperature: High temperatures may result in increased occurrence of structural adhesive joint failure, especially when acting in combination with moisture

9 Adhesive type: The chemical type of the structural adhesive plays a major role in joint durability because it determines the specific resistance of the adhesive to the various physical or chemical attack mechanisms o f the environment

9 Adherend: Structural adhesive joints to metallic adherends pose unique problems due

to the special surface properties of metals

significant tendency towards adhesive fracture in case of increased duration of water immersion and increased water temperature

Glass Facade Herz Jesu Church

In order to realize a highly durable bonding technology for the glass fagade of the Herz Jesu Church, the above listed key considerations for durability of adhesive joints were analyzed with respect to the design of the glass fagade and of the load carrying joints

Environment The arrangement of the adhesive joints in the interior of the glass facade leads

to favorable effects with respect to humidity and temperature, both of them dominated by the climate inside the building (forced air convection) Nevertheless, this type of arrangement of the glass beams was guided by architectural requirements, not by durability considerations

Adhesive Type The selection of the adhesive for the glass fagade was dominated by the structural glazing requirements posed by this kind of application Adhesives based on silicone are the only materials of choice due to their special mechanical and chemical properties Using glass as adherend, strong Si-O chemical bonds provide interracial stability with beneficial effects

on durability

Adherends The adherends, glass beams on the one hand and stainless steel channel on the other hand, are determined by the special glass facade design and can therefore not to be substituted

-Adherend Surface Pretreatment Concerning the pretreatment of the bonding surfaces, technical instructions from the adhesive manufacturer were taken into account aiming at strong and durable bonding The glass surfaces were cleaned with a special cleaning agent whereas the corresponding channel surfaces required an additional coating with a primer

Moisture/Stress / Temperature The effects of moisture, stress and temperature on adhesive joints are mainly determined by the bonding geometry Therefore, the designer of the joint has to focus on the following issues in order to increase the durability of the bonding:

9 Diminishing the attack of moisture (e.g., cleaning agents) on the bonding;

9 Obtaining a favorable stress distribution in the adhesive evoked by external loads;

9 Considering the changing temperatures causing mechanical stresses and other effects

30 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

Design of the Load-Bearing Bonding between Glass Beam and Stainless Steel Channel

An adhesive joint design that effectively addresses the above listed concerns should show the following unique features:

9 Small exposed surfaces to minimize contact of the adhesive with the environment,

9 Low loading o f adhesive and interfacial regions exposed to environment, and

9 Low shear stiffness to minimize mechanical stress induced by thermal loading

A conventional approach for bonding a steel stringer to the glass beam consists o f a steel ribbon attached at one side to the glass abutting face Nevertheless, this design shows substantial disadvantages with respect to the above-mentioned key durability concerns Under tension loading, the adhesive is strongly stressed at the interfacial regions on the bonding surface as silicone has a nearly incompressible behavior leading to lateral contractions [7] Due to the differences in the flexibility o f silicone, steel and glass (Table 1), the lateral contractions under uniaxial deformation o f the adhesive results in regions o f high strains at the edges of the structural joint (Fig 4) In this case, the following combination of critical factors suggests that this type of joint shows only limited performance with respect to durability and fracture mechanics:

9 The tension loaded surface is exposed to environmental attacks,

9 The peak loading of the interface occurs in regions exposed to the environment, this being the worst condition with respect to durability, and

9 The fracture mechanics behavior favors joint failure as crack growth leads to increasing stresses due to the diminishing load-carrying cross section area

TABLE 1 - - Physicalproperties

Young Modulus, Poisson's Ratio, Thermal Expansion,

3 Sitte, S., Dow Coming GmbH, Germany, personal communication with A Hagl, A Hagl Ingenieurgeselischatt mbH, Graefelfing, Germany, November 2002

FIG 5 - Bonding design glass fagade Herz Jesu Church

FIG 6 - - Stress distribution of three-sided bonding

9 In case o f failure or fracture in the front face region, the lateral interfaces establish a second load path by shear

In this context, it is very interesting to note that due to the high level o f incompressibility of the silicone adhesive, almost 90 % of the total load is ~ansferred by tension stresses in the front

32 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

region and the remaining 10 % by shear stresses in the side regions If lateral contraction of the adhesive were neglected (assuming constant tension stress in the front region and constant shear stress in the side regions), only 60 % of the total tension load would be transferred by the front region For this case the load is shared between front and side regions according to the Eq 1

F =F~., + C~e =(EA~" +2GA,~a~]u

k t f~ont t ~ )

(1)

This load rearrangement is evoked by the dramatically increased stiffness of the front region caused by restricting the lateral contraction of the adhesive due to the three-sided design and its encapsulating capability, see Eq 2 Please note that if a perfectly incompressible material (Poisson's ratio v = 0.5) is totally encapsulated by rigid boundaries, tension or compression stiffness is infinite, see Eq 3

Although this bonding design shows a high stiffness under tension, shear movement in the stringer direction is governed by the high flexibility of the silicone adhesive Therefore, temperature variations do not result in high shear stress in the adhesive, despite differing expansion characteristics of the materials, steel and glass; this effect also being favorable for the durability of the bond design

A critical issue for this kind of bond design is the selection of an adequate geometry (side lengths, adhesive thickness) Increasing side lengths lead to favorable encapsulating effects of the highly loaded front region with respect to diffusion of aggressive environmental media and to beneficial load carrying capabilities in case of failure of the front region The disadvantages of large side lengths are seen in aesthetic drawbacks due to increased visibility of the steel channels and in high consumption of material (steel, adhesive) Therefore, compromises have been worked out leading to the selected bonding design with a mount length (adhesive bite) of 30 mm overall The thickness selection of the bonding in the front and side regions is governed by minimum thickness requirements of the adhesive and by tolerances of the components The thickness of the adhesive is adjusted by the usage of positioning devices to 5 mm in the front and side regions

FIG 7 - - Peak stress distribution in horizontal glass beam,

Experimental Tests for Material and Design

Due to the innovative design of the bonding, an integral part oftbe glass facade certification

is dedicated to experimental tests resulting from a lack of adequate standards The European Organization for Technical Approvals (EOTA) has established rules for the application of structural sealant glazing systems According to the 'Guideline for European Technical Approval for Structural Sealant Glazing Systems (ETAG N ~ 002)', samples were mechanically tested under various conditions by the German Institut Rir Fenstertechnik Oft), Rosenheim (Fig 8) Regarding the selected material combination for the glass fafade, related tests have been successfully performed for tension and shear strength in a temperature range from -20 ~ C to +80 ~ C Furthermore, tension strength behavior has been analyzed with respect to environmental influences by artificial ageing or conditioning Therefore, samples were exposed to:

9 Ultraviolet (UV) radiation combined with immersion in water at high temperature,

9 Humidity and sodium chloride (NaCl) salt spray environment,

9 Humidity and sulfur dioxide (SO2) gas environment, and

34 BUILDING/CONSTRUCTION SEALANTS AND ADHESIVES

9 Immersion in fagade cleaning products (water/surfactant mixture)

Regarding all investigated test conditions, the samples did not show any significant decrease

in mechanical strength As the bonding design of the glass fagade differs substantially by the three-sided design from these samples (only one-sided bonding), special specimens of the envisaged design with 50 mm width were tested in order to investigate the influence o f design on bonding strength (Fig 9)

FIG 8 - - ETAG ~ 002 test specimen

FIG 9 - - Specimen design Herz Jesu Church

The samples were loaded by tension according to the critical loads encountered by the bonding in the glass facade Figure 10 shows the mechanical behavior of a sample under an enforced deformation rate of 5 mm/min At a deflection of about 2 mm, the stiffness of the sample decreases substantially although the load-carrying maximum is still not reached Based

on the FE analysis results, it is assumed that at 2 mm deflection, the bonding reaches its strength limits in the front region The failure in the tension stressed area leads to increased flexibility of the bonding and the load is increasingly transferred to the still intact side regions, which establish the load path by shear The deflection at maximum load (approximately 8 mm) confirms this hypothesis as the related strain corresponds to those experienced with ETAG specimen under maximum shear force

FIG 11 - - Maximum strength with and without continuous loading

Concerning environmental attacks, no additional tests were performed for the three-sided bonding design The critical stress factor with respect to the glass facade is the application of cleaning agents inside the building Due to the design of the bonding, it is assumed that the

36 BUILDING~CONSTRUCTION SEALANTS AND ADHESIVES

behavior of the three-sided bonding is superior to the ETAG sample with respect to environmental conditions as the highly stressed region is encapsulated Regarding the ETAG sample, load peaks are generated at edges and comers of the adhesive similar to the one-side bonding design presented in Fig 4 Therefore, the load peaks are totally exposed to environmental attack mechanisms

Summary and Conclusions

At the glass facade of the Herz Jesu Church, Munich, horizontal and vertical glass beams form major structural components designed to carry wind and dead loads The glass beams are bonded to stainless steel sections using a silicone adhesive for load transfer In order to allow for

an adequate design of the adhesive joint, a short review is presented with respect to parameters substantially affecting structural joint durability This review is discussed in the context of two possible bonding designs, a conventional one-sided bonding and a three-sided bonding finally selected for the glass fagade of the Herz Jesu Church The three-sided bonding shows advantages

in the fields of encapsulation of high stresses, low loading of interfacial regions exposed to the environment, and establishment of a redundant load path in case of primary failure Furthermore, the design of the bonding using a channel type steel section as adherend leads to beneficial effects with respect to diffusion of aggressive moisture, e.g., cleaning agents Experimental results are presented with respect to the load carrying capability of the three-sided bonding design without and with pre-loading

The innovative design of the bonding of the glass fagade of the Herz Jesu Church has focused the interest of glass manufacturers, adhesive manufacturers and civil engineers on structural adhesive jointing potential, which is not totally evaluated and exploited at the moment Therefore, the author of this article has established within the non-profit trade-organization 'glass construction ('Facbverband Konstmktiver Glasbau') a working group 'Adhesive Bonding' ('Arbeitsgruppe Verkleben'), which is dedicated to fundamental research of structural adhesive joints with respect to the load carrying bonding of glass elements to structures

References

[1] Hagl, A., "Synthese aus Glas und Stahl: Die Herz-Jesu-Kirche M0nchen," Stahlbau, Vol

71, No 7, Ernst & Sohn Verlag, Berlin, Germany, 2002

[2] Kinloch, A J (Ed.), Durability of Structural Adhesives, Elsevier Applied Science Publishers Ltd., London, United Kingdom, 1983

[3] Forschtmgs- und Materialpriifungsanstalt (FMPA) Baden Wiirttemberg, "Untersuchung des Adhasionsverlustes yon Silikonklebem durch Wasserlagerung, Berieht: 25-13035-1," Fraunhofer IRB Verlag, Stuttgart, Germany, 1996

[4] Schneider, K J (Ed.), Bautabellen ~ r Ingenieure, Wemer Verlag, Dtisseldorf, Germany,