S UMMARY AND C ONCLUSIONS

8.1 O

VERVIEW

In the present study, the behaviour and the possible failure modes of an RC wall connected with floor slabs in a typical RC frame-wall buildings, have been investigated. Displacement controlled nonlinear static analysis has been carried out on wall-slab assemblage by varying salient structural parameters. In this chapter, the summary of the study, the salient conclusions drawn and the possible future scope of work have been discussed.

8.2 S

UMMARY

The study can be summarized into the following parts:

 Finite element modelling and material validation: To achieve the objectives of the present study, finite element modelling of the multistoried building and a wall-slab assemblage is carried out. Also material model (CDP) used for the analysis is validated with an experimental study from the past research.

 Development of numerical model: To investigate the influence of floor slab on the behaviour of shear wall, a simplified and efficient numerical model is developed. The model is subjected to nonlinear static analysis to observe the extent of damage at the shear wall-floor slab junction region. Six different models are considered for the analysis, tensile damage patterns for all the models are observed and based on the observed behaviour, the numerical model of wall-slab assemblage is refined for further analysis.

 Assessment of tensile damage: By varying the aspect ratio of the shear wall panel and vertical reinforcement ratio in the wall, parametric study is carried out for the shear wall- slab assemblage. Considering different lengths of shear wall, the influence of floor slab on the behaviour of shear wall is studied. The tensile damage in the slab may extend beyond the ends of the wall on the either side, hence the floor slabs in some models are extended beyond the length of the shear wall. The behavior of the junction between the shear wall and floor slab has been studied by observing the stresses in the steel reinforcement, plastic strain, minimum principal stress, tensile damage and compressive damage patterns.

 Calculation of plastic hinge length at RC wall-slab junction: As compared to an isolated slender wall, the region of nonlinearity and inelastic actions in a shear wall will differ when connected with the floor slab at every floor level. In the present study, displacement based nonlinear static analysis of the wall-slab assemblage is carried out considering in both monotonic and cyclic modes. The axial compression on wall and the wall panel aspect ratio is varied to propose a close form equations for plastic hinge length of the shear wall when connected with the floor slab.

 Lateral drift limit for shear wall connected with floor slab: To investigate the lateral drift limit of the shear wall, parametric study of the wall-slab assemblage is performed. The primary variables are the aspect ratio of the wall panel, thickness of shear wall and thickness of floor slab. The axial load ratio, the amount of horizontal and vertical web reinforcement are kept same for all the models. A limited range of lateral drift is proposed to minimize the damage in slab and wall-slab junction of RC frame-wall buildings.

8.3 C

ONCLUSIONS

The following salient conclusions are drawn from the study:

1. Under lateral loadings, the slender wall of a shear wall-floor slab system gets partitioned into a number of smaller panels between successive floor slabs. Each such panel behaves as a squat wall with the formation of diagonal strut between two successive slab-wall junctions. Thus, the design methodology should consider strut formation and associated failure modes for slender walls in multistoried buildings with floor slabs. The strut formation leads to further propagation of damage in the floor slab.

2. The portion of the floor slab connected to the walls undergoes significant damage at higher levels of lateral displacement. Significant damage at slab-wall junction may also lead to formation of sliding shear crack across the wall. Thus, a new design methodology involving prevention or reduction of damage in slab needs to be evolved.

3. The finite element analysis results confirm that the maximum stress concentration develops at the base of the shear wall (EWSC) first and then move to the upper floor level at the junction.

Also, the developed tensile damage and the stresses are higher in the portion of the slab connected to the shear walls which are oriented in the direction of the lateral loadings.

4. As per the current provision of the Indian earthquake code IS: 1893 (Part-1)-2016, RC buildings are expected to show linear elastic behaviour till the lateral drift limit of 0.4%. However, for all the studied models, nonlinearity in concrete in wall-slab junction starts at much lower drift

levels. Also, yielding of vertical reinforcement in wall is observed at lower or comparable drift levels. Thus, the existing codal prescription needs to be relooked at for RC wall buildings.

5. The tensile and compressive damages in the slab depend on the aspect ratio of the wall panel and the amount of vertical reinforcement in the wall. It is observed that higher aspect ratio and lower reinforcement ratio resulted in maximum damage at lower values of lateral drift.

6. The plastic hinge length for wall-slab junction region increases with the wall panel aspect ratio.

A relation between plastic hinge length with monotonic and cyclic loading is developed, which is L_p,monotonic1.34L_p,cyclic

7. A lateral drift limit between 0.08% - 0.15% is recommended to avoid the damage at the junction region of shear wall and floor slab during earthquake shaking, and implementation of drift based design of rectangular shear wall is recommended. Also, recommended length of wall should not exceed 3 m along with minimum wall panel aspect ratio of 1.0.

8.4 R

ECOMMENDATIONS

S

COPE FOR

F

UTURE

W

ORK

Based on the present study, limitations of the study and future extension of this work are discussed.

In the present study, parametric studies are carried out to study the behaviour of isolated wall-slab assemblage; however the global response of RC wall-frame multistoried building need to be investigated in light of the proposed design methodology. Present study of wall-slab assemblage does not involve nonlinear analysis under ground motions, and this aspect can be further explored.

Experimental studies need to be carried out to validate the proposed equations for plastic hinge length in shear wall connected with floor slabs. Also, the proposed lateral drift criteria for shear wall buildings in the present study needs experimental verifications.