EUROPÄISCHE NORM July 2009 English Version Precast concrete products - Special roof elements Produits préfabriqués en béton - Éléments spéciaux de couverture Betonfertigteile - Besond
Material requirements
According to EN 13369:2004 4.1, the essential aspects regarding the constituent materials of concrete, as well as reinforcing and prestressing steel, inserts, and connections, must be adhered to It is crucial to take into account the ultimate tensile strength and tensile yield strength of steel.
Production requirements
Concrete production
Clause 4.2.1 of EN 13369:2004 shall apply In particular the compressive strength of concrete shall be considered.
Hardened concrete
Clause 4.2.2 of EN 13369:2004 shall apply.
Structural reinforcement
In addition to Clause 4.2.3 of EN 13369:2004, the following specific rules shall apply
Special care shall be given to ensure a stable positioning of reinforcement in the thin slabs (t ≤ 100 mm)
For welded meshes and isolated bars in thin slabs, concrete covers against formworks shall be ensured by a sufficiently dense distribution of spacers
To prevent displacements and deformations of steel reinforcement, it is essential to ensure that worker access, concrete casting, and compacting are conducted carefully, maintaining the intended positioning and shapes.
Finished product requirements
Geometrical properties
The specified production tolerances, measured in millimeters, are outlined in Figure 1 These tolerances indicate the allowable deviations from the design (nominal) values detailed in the project documentation, including any potential cambers.
Thickness "t" of thin flanges and plates (t ≤ 150)
Total depth "h" of any cross section (h < 2 500) ± ∆ h 12 + h/140
Bow horizontal mis- alignment of lateral edges ± ε L/700
For the length "L" and the reinforcement placing "c", the corresponding permitted deviation ∆ L and ∆c are given in
The tolerance for the size of holes and openings can be assumed to be 1.5 times the value of ∆b Similarly, for the overall positioning of holes and inserts, a tolerance of 1.5 times the values of ∆L and ∆b may be applied Additional values may be specified in the project documentation.
For prestressed elements 1,5 time the value of ∆v tolerance may be assumed; this includes the effects of prestressing tolerances Other values may be given in project specifications
Although production tolerances can refer to any dimension of the element, it is sufficient to follow the Standard Method of checking specified in point 5.2
Figure 1 — Measure of production tolerances 4.3.1.2 Minimum dimensions
Clause 4.3.1.2 of EN 13369:2004 shall apply.
Surface characteristics
For surface characteristics, 4.3.2 of EN 13369:2004 shall apply
Cracking in roof elements can occur not only from calculations but also during normal functioning, particularly at the end edges of ribs, intersection lines of different plates, and corners around holes or shape discontinuities If the cracks are narrow and limited in extent without causing structural issues, a simple local filling can be used to restore the surface appearance.
Completion works of ready finished elements (such as painting, waterproofing, ) are not covered by this
Mechanical resistance
For requirements on mechanical strength Clause 4.3.3 of EN 13369:2004 (referring to EN 1990:2002, EN 1992-1- 1:2004 and EN 1992-1-2-2004) shall apply, except 4.3.3.4 dealing with verification by testing
According to section 4.3.3.3 of EN 13369:2004, special roof elements with unique design models require load tests to failure on at least two full-scale specimens of any product type before production begins This initial type testing, as outlined in section 6.2, is essential to verify the reliability of the design model used for calculations.
Specific additional information are given in informative Annex C and D
Overlapped splices of reinforcement shall be located out of the areas where the full strength is needed for the resistance of the element
The minimum dimension of the concrete section must adhere to the requirement of \( t \geq 5 d_s \), where \( t \) represents the minimum local thickness of the element and \( d_s \) denotes the diameter of the overlapped bars or wires.
The minimum transverse spacing between two adjacent laps shall be ≥ 10 d s
Resistance and reaction to fire
Fire resistance, dealing with load-bearing capacity R, integrity E and insulation I of precast prestressed concrete roof elements, expressed in terms of classes, shall be defined following 4.3.4.1, 4.3.4.2 and 4.3.4.3 of
NOTE Normally, with respect to fire resistance, the separating function EI is not required for the elements of concern
For reaction to fire, 4.3.4.4 of EN 13369:2004 shall apply.
Acoustic properties
When required, the relevant acoustic properties of roof elements shall be declared following Clause 4.3.5 of
Thermal properties
Reference shall be made to 4.3.6 of EN 13369:2004.
Durability
Clause 4.3.7 of EN 13369:2004 shall apply
According to Annex A of EN 13369:2004, specifically Tables A.1 and A.2, the upper surface of roof elements with ready finished adherent covering is considered to be in ambient condition B unless stated otherwise.
Ambient condition B applies to the internal surfaces of hollow or sandwich roof elements, as well as closed box roof elements, unless stated otherwise.
For plate parts (slab conditions of A.1 of EN 13369: 2004) of roof elements the concrete cover given for reinforcing and prestressing steel in slab geometry shall apply.
Other requirements
Clause 4.3.8.1 of EN 13369:2004 shall apply
Tests on concrete
Clause 5.1 of EN 13369:2004 shall apply.
Measuring of dimensions
The Standard Method of measuring the dimensions related to the production tolerances of 4.3.1.1 is specified below
Measurements of the demoulded finished element are conducted, excluding the reinforcement position The total length “L” is measured according to the technical specifications, with three readings taken: one at each edge and one at the center The total width “b” is assessed at three cross sections—two near the ends and one at midspan Thicknesses “t” are recorded at the same three cross sections, focusing on critical slab positions as specified, ensuring at least one measurement for each lateral flange The total depth “h” is measured using external collimator systems at the same cross sections Bow misalignment “ε” is evaluated at midspan for each lateral edge relative to its endpoints Camber “v” at midspan is compared to the design camber \(v_o\), adjusted for computed deformation \(v_c\) due to applied loads, with the relationship \(\Delta v = v - v_o - v_c\) Finally, concrete cover is measured at the lower side of the lateral flanges in critical positions, ensuring at least one measurement for each lateral flange at the three cross sections.
For the measurements above listed (at least for items a, b, e and f), the element shall be set in an arrangement as similar as possible to its final position in the structure
Following the special features of the products, proper adaptations and variations to the Standard Method can be given by the technical specifications of the product
The reinforcement position, together with the setting of prestressing tendons and special devices, is verified following the pertinent items of Table D.3.2 in Table D.3 of EN 13369:2004.
Weight of the elements
Clause 5.3 of EN 13369:2004 shall apply.
Load test of elements
Annex E gives the standard method for flexural load tests on full scale specimens of roof elements
General
Clause 6.1 of EN 13369:2004 shall apply.
Type testing
Clause 6.2 of EN 13369:2004 shall apply.
Factory production control
NOTE The missing numbers correspond to the clauses of EN 13369 included in the general references made in this subchapter
Clause 6.3 of EN 13369:2004, except 6.3.6.5, shall apply
Compliance verification of finished products will be conducted in accordance with items 3 to 5 of Table D.4.1 of EN 13369:2004, as well as the control chart outlined in Table 1 of this document Additional verifications may be carried out when specific needs arise.
The checks shall be carried out at the earliest time possible, preferably in the factory, and never after the precast units have been received and accepted at the site
Subject Aspect Method Frequency Registration
Elements surface finish visual inspection every element notice of imperfections
Elements total length see point 5.2(a) every 10 elements notation in the record form
Elements thickness see point 5.2(c) every 10 elements notation in the record form
Elements concrete cover see point 5.2(g) every 10 elements notation in the record form
Elements camber * see point 5.2(f) every month or 1/100 elements notation in the record form
Elements other production tolerances see point 5.2(b)-(d)-(e) every year or 1/600 elements notation in the record form
Elements (all types) mechanical strength
(failure conditions) see Annex E initial type tests on 2 elements proper report
Annex C) mechanical strength (service conditions) see Annex E every 6 months on 1 element proper report
The manufacturer is responsible for maintaining records of produced elements, including position number, casting date, and construction data, for the mandated archiving period and must provide access to these records upon request.
Clause 7 of EN 13369:2004 shall apply
NOTE For CE marking see Annex ZA
The technical documentation must detail the element's geometrical data and material properties, including construction data such as dimensions, tolerances, reinforcement layout, concrete cover, and anticipated support and lifting conditions.
The composition of technical documentation is given in Clause 8 of EN 13369:2004
As shown in Figure A.1, the internal actions transmitted along the thin walls of a shell structure are represented by eight components referred to its middle surface:
The above components are referred to the unit width and represent the proper integral over the plate thickness t of the stresses σx, σy, τxy, τzx, τyz
The first three components n x , n y , n xy are related to the extensional behaviour of the plate, the remaining five m x , m y , m xy , q x , q y are related to its flexural behaviour
Figure A.1 — Components of internal actions
The current standard focuses on roof elements that span primarily in one direction between two end supports In this longitudinal direction, it draws parallels to traditional beam theory, incorporating three key components: M.
The internal force components V and T correspond to the current cross-section, as illustrated in Figure A.2 These components reflect the overall impact of vertical loads, highlighting their flexural action and potential eccentricity.
When represented by an applied force, prestressing force P can be added with its eccentricity e p
Local and transverse effects due to the warping of the cross section and to the deformation of its profile are not provided by this representation
Figure A.2 — Components of the internal force
Figure B.1 - Types of simple wing-elements
B.2c - Sandwich one-rib elements Figure B.2 - Types of one-rib wing-elements
B.3c - Straddle two-ribs elements Figure B.3 - Types of two-ribs wing-elements
B.4c Figure B.4 - Types of box-elements
B.5c Figure B.5 - Types of roof-light shed-elements
B.6c - Shed folded-plate elements Figure B.6 - Types of folded-plate elements
B.7.3 - Sandwich paraboloid elements Figure B.7 - Paraboloid-elements
6 Skylight sheets (added in situ)
Figure B.9 - Typical ready finish of the product
The examples given in Annex B for roof elements and their ready finish are not intended to cover all the possible types of common production
Roof elements can be classified based on their flexural behavior and combined twist actions into several categories: a) core-beam elements, featuring a central solid core or box profile that allows for the development of tangential stresses and provides torsional resistance; b) biflexural-beam systems, where twisting actions are countered by two opposing flexures applied to longitudinal ribs; c) folded-plate systems, consisting of three or more non-convergent plates that create a complex combination of flexures; d) star-plate systems, such as V or Y profiles, where plates converge at a single axis, resulting in twisting moments; e) special-shape elements, which include unique designs like hyperbolic paraboloids with prestressing tendons aligned along the surface; and f) integrated systems, such as sandwich elements, which enhance structural resistance through complementary components.
With reference to the transmission of vertical loads to the end supports, the following two principal types of elements can be distinguished
Web-shear systems, where the presence of vertical or quasi-vertical webs extended till over the bearings allows a beam-like transmission of the shear forces over the supports
Arch-tie systems, where the longitudinal shape, with possible variable depth, leads to an arch mechanism connected with the lower tie of the incorporated reinforcement
Other special types of elements can be produced and properly designed to allow the transmission of vertical loads to the end supports through different mechanisms (e.g suspension systems, )
With reference to the U.L.S - Ultimate Limit State to be verified by calculation and testing in order to ensure the due resistance of the elements, the following cases are distinguished
For types "a" and "b" of C.1 the ordinary beam-model covered by EN 1992-1-1 can be in general applied with proper verifications
Figure C.1 — Types of roof elements
Deviations in the ultimate mechanism of maximum bending moment sections may arise from the small thickness of the compression wings This can be validated through initial type testing, including load tests to failure, and represented using a modified constitutive law for concrete, incorporating an additional γ′ c factor and/or reduced εcu deformation These modifications should be applied in standard equations for subsequent routine calculations.
Other possible deviations (e.g for shear and torsion) can be pointed out on the basis of the experimental results of the initial type testing
The transverse flexural effects of loads, such as the fixed-end bending moments of cantilever wings, can be calculated and verified locally, complementing the primary longitudinal calculations (refer to Annex D).
For type "c" of C.1 a complete "folded-plate" analysis shall be performed, inclusive of transverse flexural effects due to loads and to the deformation of the cross profile
This analysis can be referred to an elastic model comprehensive of the extensional and flexural behaviours of the plates
Finite Strip method can be applied for units with constant cross section or, in the general case, Finite Element method can be applied
The response of the above analytical models defines the distribution of the internal actions in terms of the eight components listed in A.1
For U.L.S a local verification will be consequently made following the criteria of Annex D
For regular shapes, a beam-like routine can be established to analyze the primary longitudinal behavior, which can be refined using results from initial calculations based on more accurate analytical models Additionally, transverse flexural effects can be represented through tables derived from these initial calculations.
In any case the analytical models and their possible routine simplified derivations shall be verified by initial type testing (load tests up to failure)
Roof elements classified as type "d" in section C.1 can be designed using a standard beam model, which is adjusted based on initial type testing that includes load tests to failure This process is complemented by verifying the transverse flexural effects as outlined in section C.2.2.
The torsional resistance of plates is crucial for stability, so the detailing of members must align with the design criteria specified in EN 1992-1-1 Two solutions can be selected to achieve this.
To achieve uncracked behavior in the ultimate limit state, it is essential to proportion members and apply prestressing in such a way that the principal tensile stress of the concrete remains below the design strength, ensuring that \$\sigma_I < f_{ctd}\$.
providing each slab for torsion reinforcement made of transverse closed stirrups and longitudinal bars, so to ensure a peripheral truss mechanism at the ultimate cracked state
U.L.S verifications are conducted based on the principal compression stress of concrete as outlined in Annex D, while in another scenario, these verifications utilize the equations specified in Clause 6.3 of EN 1992-1-1.
Since "star-plate" systems can have high deformability for torsion, special care shall be given to check the compatibility of twist rotations in service conditions
Unconventional "e" types of roof elements must undergo specialized analytical investigations and combined initial type testing, including load tests to failure, to ensure that their resistance checks provide a reliability comparable to traditional design models.
Non-structural components of roof elements, like upper rigid covering layers, can establish a stable connection with the structural parts, significantly enhancing their resistance This contribution is relevant for Ultimate Limit State (U.L.S) verifications when specific conditions are met.
the completion part has a documented systematic adequate resistance at least of the same reliability and durability as for the structural part;