Nghiên cứu thực nghiệm cơ chế phá hủy của kết cấu sàn phẳng bê tông cốt thép khi mất cột biên TT TIENG ANH

TRAN, QuocCuong EXPRIMENTAL STUDY ON THE COLLAPSE RESPONSE OF REINFORCED CONCRETE FLAT SLAB STRUCTURES SUBJECTED TO PERIMETER COLUMN LOSS Major: Construction engineering Code: 9580201 S

TRAN, QuocCuong

EXPRIMENTAL STUDY ON THE COLLAPSE RESPONSE OF REINFORCED CONCRETE FLAT SLAB STRUCTURES SUBJECTED TO PERIMETER COLUMN LOSS

Major: Construction engineering

Code: 9580201

SUMMARY OF DOCTORAL THESIS

Hanoi-2021

Supervisors 1: Associate Professor Ph.D PHAM XuanDat

Supervisors 2: Associate Professor Ph.D NGUYEN TrungHieu

Reviewer 1: Associate Professor Ph.D.TRAN Chung

Reviewer 2: Associate Professor Ph.D TRAN The Truyen

Reviewer 3: Ph.D NGUYEN Dai Minh

The Phd thesis will be defended by School-level committee meeting at Hanoi Uni- versity of Civil Engineering on day month year

This thesis can be found at the National Library and the Library of Hanoi University

of Civil Engineering

cially for supermarkets and sport centres Compared with the traditional build- ing beam-slab structure, the advantage of the flat floor structures is that it is easy to construct, with greater clear floor heights However, flat slab structures are prone to progressive collapse due to their relatively heavy self-weight and susceptibility to punching shear failure Therefore, the current study with a tit- tle: “Exprimental research of collapse behavior on reinforced concrete flat slab structures subject to boundary column loss” was selected to investigate the structural behaviour of flat slab structures following a column removal so that the progressive collapse of such common building structures can be miti- gated

2 Research objectives

• To construct innovative experimental models that can examine both static and dynamic behavior of flat slab structures subjected to a sudden col- umn loss

• To identify and evaluate the secondary load-carrying mechanisms in flat slab structures following a column removal

• To identify and evaluate the dynamic increase factor (DIF) in flat slab structures following a column removal

• To construct a simplified analytical model that can assess the collapse resistance of flat slab structures following a column removal

3 Scope of work

The collapse behaviour of reinforced concrete (RC) flat slab structures without drop panel The accidental scenarios selected for this research are the loss of either penultimate or perimeter column

4 Academic basic of research (Justification of the experimental investigation)

• Previous studies, both experimental and numerical, on the progressive collapse behavior of reinforced concrete building structures

• Previous research, both experimental and numerical, on the large defor- mation response of reinforced concrete structures

5 Research methodology

The methodology used in this reasearch is the combination of experimental and theoretical studies

2

6 scientific and practical significance of study

This research has provided valuable insights in the collapse behaviour of flat slab structures following a column removal Also, it has provided a simpli- fied analytical model that is able to assess the collapse resistance of flat slab structures in such accidental scenarios

7 News research’s results

• This research has successfully constructed innovative experimental mod- els that are able to examine both static and dynamic responses of flat slab structures subjected to a sudden column loss

• This research has successfully identified and evaluated the secondary load-carrying mechanisms in flat slab structures following a column re- moval

• This research has successfully identified and evaluated the dynamic in- crease factor (DIF) in flat slab structures following a column removal

• This research has successfully constructed a simplified analytical model that is able to assess the collapse resistance of flat slab structures follow- ing a column removal

8 Outline

getting starded :

TANCE OF FLAT SLAB STRUCTURES SUBJECTED TO COLUMN LOSS

Conclusion : Conclusion and future works

CHAPTER 1 RESEARCH OVERVIEW ON RESPONSE OF

REINFORCEMENT CONCRETE FLAT SLAB UNDER

BEARING COLUMN LOSS This chapter will present the contents of building’s progress collapse due to the loss of a bearing column, the mechanisms of the structure in the large deformation and related studies updated in the world as well as in Vietnam

1.1 Progressive collapse of RC building

1.1.1 Progressive collapse concept

Progressive collapse is a situation where local failure of a primary structural component leads to the collapse of adjoining members which, in turn, leads to ad- ditional collapse Hence, the total damage is disproportionate to the original cause

(a) Location of the bomb explosion (b) After the explosion (photo Reuters)

Figure 1.1: Murrah building before and after having a Progressive collapse [21]

• The direct pressure of the car bomb can only destroy the G20 column and a small part of the floor area

• The loss of bearing capacity of the transfer beam on the third floor due to the failure of the G20 column is the main cause of the collapse of half of the building

1.1.2 Mechanisms of progress collapse of RC structure in column loss case

In column loss accident, the structure will be in a state of large deformation and

it may lead to the risk of progress collapse due to the following effects:

• The double span effect is shown in Figure 1.2

Figure 1.2: Increased internal force in two-span flat beams without support [45]

• Dynamic effects is illustrated in Figure 1.3 The dynamic coefficient Ω (dy- namic increast factor (DIF)) takes into account the amplification of the load

the dynamic coefficient is represented by equation (1.1)

4

Figure 1.3: Idealization of a typical floor [44]

1.2 Behavior of flexural reinforced concrete structures in high strain state and secondary load-bearing mechanisms

1.2.1 Behavior of flexural reinforced concrete structures in high strain state The secondary bearing mechanisms are illustrated in Fig 1.4 The formation and

Figure 1.4: Compression arch action (CAA) and catenary action (CA) [37]

development of compression arch action and catenary action in a state of great de- formity is the main topic in research in the field of progressive collapse prevention 1.2.2 The secondary bearing mechanisms

• Compression arch action (CAA) is illustrated with reinforced concrete beams restrained at both ends and subjected to uniformly distributed load q as shown

Figure 1.5: Compression arch action [43]

Figure 1.6: Comparison of bearing capacity of catenary action and flexible action [43]

The working mechanism of the slab when the deformation is large, the membrane effect can be classified into three different forms:

• Compressive membrane action, Figure 1.9(a);

• Tensile membrane action, Figure 1.9(b);

• Tensile membrane action together with the development of a compressive ‘ring’ The conditions under which the membrane action occurs, including the tensile mem- brane action in the center, and the compression membrane action at the edges of the slab during large displacements, are summarized in Figure 1.8 Due to the reaction

of the joint at the two ends of the floor, a developed compression arch can signifi- cantly improve the load-carrying capacity of the slab [25] and thereby increase the load resistance of the structural system

1.3 Research on reinforced concrete structures when losing bearing columns

in the world and VietNam

1.3.1 Experimental research

Sasani et all (2007) [48] studied with the load diagram shown in Figure 1.10(a) Tuan Pham (2017) [54] Research on 2D beam to clarify formation, development and load resistance of alternative load path, Figure 1.11(a)

Dat Pham (2015) [45] tested 12 samples of reinforced concrete beam floor struc- ture, Figure 1.11(b)

Gouverneur (2014) [25], experimental research on three reinforced concrete slab samples, experimental model and loading diagram are illustrated as Figure 1.12

6

Figure 1.7: Formation of membrane action in RC flat slab structure [41]

Figure 1.8: Types of membrane effects of flat slab structure [25]

(a) Compressive membrance action (b) Tension membrance action

Figure 1.9: Membrance action of restrained slab[25]

Figure 1.10: Alternate load path in reinforced concrete beam [48]

Russell Justin (2015) [46], University of Nottingham, UK Experimental study (static and dynamic) of flat floor structure without bearing columns

QianKai and Li Binh (2016) [30] conducted an experiment on flat floor structures subjected to central column loss The test floor structure is loaded until it completely

(a) Concrete beam structure [54] (b) RC floor beams Structure[44]

Figure 1.11: Experiment of RC floor beams without a boundary column

Figure 1.12: Experiment to evaluate the membrane action of flat floors [25] collapses to determine an alternative load path

1.3.2 Semi-empirical methods for calculation of building collapse resistance Izzudin and all proposed a computational model like Figure 1.13 [20] When

Figure 1.13: Simple dynamic evaluation method [20]

be calculated by equalizing the area of the two figures shaded in Figure 1.13b, These areas represent the work of a static and dynamic external force

Pham.X.D et al (2015)[44] have introduced a simple method to rapidly evaluate the load resistance of double span reinforced concrete beam-floor structures This equivalent one-degree-of-freedom system has a simplified stiffness and displacement

8 relationship as elastic-plastic The load resistance function R of the structural system

is built based on two specific parameters presented in Figure 1.14

Figure 1.14: Elastic-plastic relationship of RC structure at frame node[44]

1.4 Chapter summary and conclusion

• Progressive collapse will be prevented if the collapse of the first floor structure continues after local failure does not occur

• Miniature experimental model is a suitable method in laboratory conditions and is reliable within the scope of the doctoral thesis

• Although there are quite a few empirical studies related to the reinforced con- crete flat floor structure (the field of Progressive collapse) have been published recently, but these studies still have incomplete points

• Developing a simple and reliable calculation method for flat-floor structures is necessary to assist engineers in practice during the structural planning phase

CHAPTER 2 EXPERIMENTAL RESEARCH ON MODEL OF RC FS

SUBJECT TO BOUNDARY COLUMN LOSS The behavior of the reinforced concrete floor structure when losing a boundary column will be determined through experimental research on model objects in the laboratory Two case studies were including:

1 Static test, carried out with two samples of reinforced concrete flat slab lost before a load-bearing column is slowly loaded until failure

2 Dynamic test, conducted on a reinforced concrete floor slab with a sudden column loss while under the impact of the sevice load

3 Analysis of test results as a basis for building a semi-empirical formula

4 Clarifying the working mechanism of the reinforced concrete floor when the deformation is large

2.1.2 Contents of experimental research

• Design and set up concrete slabs and 3D structural models according to the design parameters of a prototype building

• Design of loading system, load generation methods, arrangement of tools and measuring equipment

• Experimental survey of parameters reflecting the specimen behavior

• Observe the formation and development of cracks, failure mode

2.2 Experimental model building base

• Comply with the criteria of similarity theory: similar in geometrical dimen- sions, similar in materials, similar in bonding conditions

• Suitable space and laboratory conditions

2.3 Experimental model and fabricated materials

2.3.1 Experimental model

Fig 2.1 is the experimental model that has been designed and built The number

of samples and sample name in Table 2.1

Table 2.1: Statistics of experimental samples

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Figure 2.1: Experimental model

Cimen

PCB40 (kg)

sand (kg)

Stone 1x2 (kg)

Water (lít)

Compressive strength R28 (MPa)

2.3.2 Material properties

• Concrete grade is determined in Table 2.2

• The test results of concrete reinforcement are presented in Table 2.3

Table 2.3: Material properties of concrete reinforcement

The static test is performed with the test specimen loaded when one of the sup- porting columns is lost (the model has only 5 support columns) In Figure 2.2 is the experimental layout with the load application diagram performed through 24 load points and the load distribution mechanism by 3-legged support systems

cONCRETE CUBE 150x150 mm

LOADING PLAN

SECTION LAYOUT 24 LOAD POINTS LOADING PLAN

SECTION LAYOUT 24 LOAD POINTS

Figure 2.2: Loading diagram and plan 24 load points

2.5 Dynamic test load

Figure 2.3 depicts the strut structure (temporary pillar) The SP2 sample for dy- namic testing has enough columns to support the load, which is statically loaded to

sive collapse resistance The basis for determining the value of the load acting on the floor slab when the column is lost includes:

• Based on the design load of the ductile method, the maximum load resistance

of the reinforced concrete slab floor is calculated when the bearing column is lost (large deformation);

• Consistent with the results of static test load performed with sample SP1

12

Figure 2.3: Column system replaced by steel column 2.6 Measuring devices and instruments

2.6.1 Displacement measuring devices and instruments

Diagram of displacement measuring device is arranged as in Figure 2.4 The LVDT1, LVDT3, LVDT5 measure vertical displacement, two LVDT2, LVDT4 mea- sure horizontal displacement

Figure 2.4: Layout of displacement measuring device (LVDT)

Using a strain gauge (resistor plate) includes the following objectives:

• Measure the axial strain of steel support columns;

Mặt bằng vị trí các phiến điện trở được trình bày như Figure 2.5 Các phiến điện trở được đánh số từ 1 đến 15 The location plan of the resistor plates is presented as Figure 2.5 The resistor plates are numbered from 1 to 15 Figure 2.6 shows how to

Locaton of strain gauge lower layer

Locaton of strain gauge upper layer Locaton of strain gauge lower layer

Locaton of strain gauge upper layer

Figure 2.5: The layout of the resistor plates measure the internal force in each steel column (C-1 to C-5) The internal force in

Figure 2.6: Layout diagram of steel column internal force measuring device

the column is calculated from the deformation data in the experiment according to the formulas (2.1), (2.2), [42], [43], [44]:

14

∗

inertia and the outer radius of the steel column, respectively

2.7 Chapter conclusion

• Miniature experimental model has been set up with 1/3 of the actual size

• A suitable static and dynamic load method has been designed to allow static and dynamic tests to be performed

• The measuring instruments and equipment have been arranged to allow the evaluation of the test sample behavior

CHAPTER 3 ANALYSIS AND ASSESSMENT OF

EXPERIMENT RESULTS This chapter presents experimental results, including static and dynamic experi- ments Samples SP1, SP3 static testing Sample SP2 was dynamically tested due to sudden column loss

3.1 Analysis of static test results with samples SP1 and SP3

3.1.1 Crack distribution, pattern and failure mechanism of the test sample

The crack distribution diagram of SP1, SP3 test samples is shown on Figure 3.1 The order of appearance of cracks (1), (3), (2), (4), (5), (6) Cracks on the underside

Vết nứt trên 2,4,5,6 Vết nứt dưới 1, 3, 7

(a) Sample SP1

Vết nứt trên 2,4,5,6 Vết nứt dưới 1, 3

(b) Sample SP3

Figure 3.1: Diagram of crack development and failure mode of the test specimen

of slab (1), (3), cracks on the top side of slab (2), (4), (5), (6)