An analytic Study on a New Semi-Rigid Infilled Shear Wall

*Murat Arda Uğurlu1), Abdulhalim Karaşin2), Halil Görgün3) and Sultan Erdemli Gunaslan4)

1),2),3), 4) Department of Civil Engineering, Dicle University, Diyarbakır, Turkey

3) hgorgun@dicle.edu.tr

ABSTRACT

Infill walls are the most common separator panel in the reinforced concrete frame structures. Due to the materials used, in most cases such structural elements have considerable resistance capacity against vertical and lateral loads. Therefore it is very important to understand the characteristics of infill frame structures. Despite infill walls have significant contributions to the behaviour of the structure under lateral and vertical loading, in designing procedures, in many cases the strength characteristics of such infill wall materials is assumed to be of no contribution. The new proposed semi rigid shear wall is assumed to provide many advantages in construction engineering. The objective of this study is to determine analytical behaviour of the new semi-rigid infill for single storey - single bay reinforced concrete frame to compare with different known types of masonry infills under quasi-static loading conditions. The dynamic parameters of the reinforced concrete frames with masonry infill walls are modeled analytically with software packages. Results obtained from different frames that consist of standard brick infilled and reinforced infilled semi-rigid walls are compared with each other with respect to strength, stiffness and energy related parameters. It is concluded that the new semi-rigid shear wall models have great advantages both in strength capacity and practical solution for shear wall construction. 1. Introduction

The most common type structural system in Turkey for both residential and office buildings is multi-level reinforced concrete frames with masonry infill walls. In designing procedure of reinforced concrete frame structures with masonry infill walls, the strength characteristics of infill materials usually assumed to be of no contribution except for its weight are not excessively emphasized. Infill wall has actually significant contributions to the behaviour of the structure under earthquake and vertical loading, and the dynamic characteristics such as stiffness, bearing capacity, period, and damping [FEMA].

1), 4)

Ph. D. Student 2), 3)

Associate Professor.

As the computational and experimental methods have improved, the great deal of research work have been done on the masonry infilled reinforced concrete frames during last several decades. Holmes (1961) investigated the behaviour of infilled (brick and concrete) steel frames by using small-scale, single bay and single-storey specimens and used an equivalent diagonal strut to model the wall panel. Mallick and Severn (1967) used finite element methods to determine the stiffness of infilled frames. Klinger and Bertero (1978) investigated the hysteretic behaviour of masonry infilled RC frames and concluded that RC frames with masonry infills have better energy dissipation capacity and strength properties than frames without masonry infill walls. Gulkan and Wasti (1993) investigated the nonlinear behaviour of one bay-one storey RC frames with different storey heights using finite element methods and they have concluded that ignoring the effect of masonry infilled walls inside frames in the calculation of the natural periods of structures can be erroneous. Mehrabi, Shing, Schuller and Noland (1996) examined the effect of infill walls on the seismic performance of reinforced concrete frames. They stated that failure and frame panel interaction was governed by relative strengths of the panel and the frame. Mosalam, White and Gergely (1997) examined unreinforced solid concrete masonry infilled gravity load designed steel frames under quasi-static cyclic lateral loads. They stated the width of equivalent strut was not uniform; it decreased towards the loaded corners and proposed a hysteresis model. Sahota & Riddington (1998) showed that using a copper-tellurium lead layer increased the cracking load of the tested infill but neither changed the ultimate strength so much nor had any adverse effect on the cracking performance of the infilled frame. Crisafulli, Carr and Park (2000) proposed an approach using the principles of capacity design, a new design approach is proposed for cantilever infilled frames, in which the ductile behaviour is achieved by controlled yielding of the longitudinal reinforcement at the base of the columns. Marjani and Ersoy (2002) investigated the seismic behaviour of masonry infilled RC frames by an experimental program composed of six one bay-two storey frames. The experimental results showed that using clay hollow brick infill increased both the strength and stiffness values compare to their bare frame counterparts. Aref and Jung (2003) proposed a new infill panel, composed of polymer matrix composite (PMC) material. It was shown that the introduction of a PMC infill wall in a semi-rigidly connected steel frame produced significant enhancements to the stiffness, strength and energy dissipation. Moghadam (2004) introduces a new analytical approach for the evaluation of shear strength and cracking pattern of masonry infill panels. This method is based on minimizing the factor of safety with reference to the failure surfaces. Taher and Afefy (2008) presented a comparison between nonlinear analysis for RC frame with masonry infill panels modeled as a whole and infill panels modeled as unilateral diagonal struts where each strut activated only in compression. The results of this study showed the significance of infill walls in increasing the strength, stiffness, and frequency of the entire system depending on the position and amount of infills. Mohammadi and Akrami (2010) presented a paper of the results of an experimental investigation on some engineered infilled frames with high ductility and adjustable strength. The results show that the engineered infilled frames have adjustable strength, as well as high ductility and damping.

In this study a new proposed semi rigid shear wall is designed to provide advantages in strength capacity and practical solution for shear wall construction. The objective of this study is to determine analytical behaviour of the new semi-rigid infill for single storey - single bay reinforced concrete frame to compare with different known types of masonry infills under quasi-static loading conditions modeled analytically with software packages. Results obtained from the different frames that consist of standard brick infilled, bare frame, and reinforced infilled semi-rigid walls are compared with each other with respect to cyclic loading and pushover analysis as strength, stiffness and energy related parameters. 2. Geometrical Descriptions The geometry of the single storey - single bay reinforced concrete frame as a standard bare frame with 250x500 mm columns dimensions and 250x400 mm beam dimensions is illustrated in Fig.1. The frame is denoted to be reference frame for the other infill frames namely standard brick infilled, bare frame, standard shear wall and reinforced infilled semi-rigid wall.

Fig. 1 Dimensions of the reference bare frame.

The reinforcement details and dimensions of all test specimens of the new semi-rigid shear wall is shown in Fig.2. The infills of the frame consist of bricks with hallov core as shown in Fig. 3(a). reinforced with vertical rebars from bottom of the frame to 50 cm over the beam level. This continuous core hollow monoliticaly infiled by fresh concrete simultaneously with columns and beam.

Fig.2 The new semi rigid shear wall frame.

The size of the brick which may be produced specifically with the 25 cm x 49 cm dimensions as shown in Fig. 3(b). Between brick layers vertically 1 cm gap considered for mortar layer is aimed to provide continuous vertical small columns of 15 cm x 15 cm. The countinious small columns inside the bricks provide significantly differ from standard bricks in terms of the way they are used for constructing infill walls. The other infills of the standard brick infilled frame (SBF) and standard shear wall (SSW) are assumed to have the same dimensions.

Fig. 3 Proposed brick: a) 3D solid model, b) dimensions.

3. Analytical Study In order to discuss and compare the performance of the new semi-rigid shear wall it is proposed to determine the behaviour of standard brick infilled frame (SBF), bare frame (BaF), standard shear wall (SSW) and the new semi-rigid wall (SRSW) frames with single storey and single bay under lateral in plane loading. The pushover analysis and reversed cyclic static load (quasi-static loading) have been performed to compare the 4 reinforced concrete frames.

For the four cases the frames were modeled with finite element software Seismostruct V5 (Seismosoft, 2016). Fibre based modeling of cross-section behaviour is used, where each fibre is associated with a uniaxial stress-strain relationship in Seismostruct. Mander concrete model was used for both confined and unconfined concrete sections while steel model was selected as Menegetto-Pinto steel model with Monti-Nuti post-elastic buckling model. Following parameters were the same for both confined and unconfined concrete. The mechanical properties for concrete and steel model are given in Tables 1-2. Seismostruct has an confinement factor calculation module which calculate confinement factor with the properties of hoops and longitudinal reinforcements. Table 1 Mechanical properties of of Mander et. al. (1988) nonlinear concrete model

Mechanical Properties Concrete Model

Compressive Strength (MPa) 33.00

Tensile Strength (MPa) 3.30

Modulus of Elasticity (MPa) 27000.00

Strain at Peak Stress (mm/mm) 0.002

Specific Weight (kN/m3) 24.00

Table 2 Mechanical properties of Menegotto-Pinto (1973) Steel Model

Mechanical Properties Steel Model

Modulus of Elasticity (MPa) 200000.00

Yield Strength (MPa) 575.00

Strain Hardening Parameter (-) 0.005

Transition Curve Initial Shape Parameter (-) 20.00

Transition Curve Shape Calibrating Coefficient A1 (-) 18.50

Transition Curve Shape Calibrating Coefficient A2 (-) 0.15

Isotropic Calibrating Coefficient A3 (-) 0.00

Isotropic Calibrating Coefficient A4 (-) 1.00

Fracture/Buckling Strain (-) 0.10

Specific Weight (kN/m3) 78.00

The model parameters of infill panel and infill panel strut curve parameters for standard infilled frame and the semi-rigid shear used in analysis are given in Tables 3-4. Table 3 Infill panel parameters for standard infilled frame and the semi-rigid shear wall

Model Parameters Standard Infilled Frame Parameters

The Semi-Rigid Shear Wall Parameters

Panel Thickness – t (m) 0.25 0.25

Out-of-Plane Failure Drift (%) 5.00 5.00

Strut Area 1 (m2) 0.044685 0.044685

Strut Area 2 (%) 40.00 40.00

Equivalent Contact Length (%) 23.00 23.00

Horizontal Offset (%) 2.40 2.40

Vertical Offset (%) 10.00 10.00

Proportion of Stiffness Assigned to Shear (%) 60.00 60.00

Specific Weight (kN/m3) 14.00 17.635

Table 4 Infill panel strut curve parameters for standard infilled frame and the semi-rigid

shear wall

Model Parameters Standard Infilled Frame Parameters

The Semi-Rigid Shear Wall Parameters

Initial Young Modulus (MPa) 700.00 14290.00

Compressive Strength (MPa) 1.1 12.653

Tensile Strength (MPa) 0.00 0.00

Strain at Maximum Stress (mm/mm) 0.0012 0.0012

Ultimate Strain (mm/mm) 0.015 0.015

Closing Strain (mm/mm) 0.004 0.004

Strut Area Reduction Strain (-) 0.0006 0.0006

Residual Strut Area Strain (-) 0.006 0.006

Starting Unloading Stiffness Factor (-) 1.50 1.50

Strain Reloading Factor (-) 0.20 0.20

Strain Inflection Factor (-) 0.70 0.70

Complete Unloading Strain Factor (-) 1.50 1.50

Stress Inflection Factor (-) 0.90 0.90

Zero Stress Stiffness Factor – γplu (-) 1.00 1.00

Reloading Stiffness Factor – γplr (-) 1.10 1.10

Plastic Unloading Stiffness Factor – ex1 (-) 3.00 3.00

Repeated Cycle Strain Factor - ex2 (-) 1.40 1.40

All of these parameters are within recommended values of earlier studies Ugurlu(2011) and Mısırlı et.al. (2012). Other parameters were taken as default values. Inelastic displacement-based frame element model is used to model beam and column elements. Nodes at the foundation level were fixed in all directions. Three reversed quasi-static cyclic analyses were made; bare frame, standard brick infilled frame and the new semi-rigid brick infilled frame. The loading protocols applied as top drifts are the same for the frames and analytical models as shown in Fig. 4.

Fig 4. Loading protocol for quasi-static cyclic analysis

The finite element package Seismostruct seams to be successful at predicting the large displacement behaviour of frames under static or dynamic loading while taking into account both geometric nonlinearities and material inelasticity. Base shear vs. roof drift relationships of Bare brame, standard brick infilled frame and the new semi rigid brick infilled frame were compared analytically in Fig. 5. The comparision of the same frames and the standard shear wall frame are given in Fig. 6.

Fig. 5 Comparison of cyclic loads of the bare frame, standard brick infilled frame, the

0 25 50 75 100-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

Step Number

Drift R

atio, [%

]

semi rigid shear wall and standard shear wall.

Fig. 6 Analytical comparison of pushover behaviour of the bare frame, standard brick

infilled frame, the semi rigid shear wall and standard shear wall. 4. Conclusions In this study, three one bay-one storey reinforced concrete frames with different

masonry infill wall conditions are tested under cyclic loading. Results are presented in

terms of force – interstory drift ratio, stiffness degradation, and cumulative energy

dissipation ratio plots and comparisons are made.

The presence of the new semi-rigid masonry infill walls effects the seismic behaviour of framed building to large extent. These effects are generally positive based on the type of masonry infill wall used. The semi-rigid masonry infill walls performed between standard shear wall and ordinary masonry infill walls by means of global stiffness and strength of the structure as expected. The analytical results show advantages of the semi rigid shear wall frame clearly.

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