Journal Aug 2021

Seismic performance evaluation of framed RC building with and without ductile detailing Madheswaran C. K., Gopalakrishnan N., Prakashvel J., Sathishkumar K.

Two three-storey half-scale Reinforced Concrete(RC) building, are designed and constructed to study its seismic response characteristics. First framed RC building is designed without ductile detailing. Second building is designed with ductile detailing as per IS13920 code. Experimental studies are carried out using the 4m × 4m tri-axial shake-table facility to evaluate the seismic performance of RC building without and with ductile detailing. The seismic performance of the ductile detailing over the non-ductile detailing is studied. The earthquake excitation is given for both cases. All the displacements, acceleration and strain responses are measured along the direction of table excitation. Failure behaviour of the both RC buildings are presented.

Seismic safety of 4 storey reinforced concrete open ground storey structure Swajit Singh Goud, Ramancharla Pradeep Kumar

Earthquake safety of buildings is one of the primary concerns of structural engineers throughout the world. The performance of buildings during past earthquakes has brought out the lacunas in design, analysis and execution of these structures. The constant endeavour for uniqueness has led to the distribution of irregularities along the plan and height of buildings. One of such attempts is the development of Open Ground Storey (OGS) buildings. It is the dominant parameter having vertical irregularity, if not rectified, may often lead to the collapse of structure. Reinforced concrete building with OGS; absence of infill wall in a ground storey, is prevailing construction practice in most places in India. It causes a sudden decrease in lateral stiffness (K) and strength (V), from adjacent upper to ground storey, results in accumulation of stresses due to large lateral displacement in ground storey columns to cause soft storey effect. The problem can be solved by increasing K and V of the ground storey relative to the adjacent upper storey. Seismic codes specify the design process for buildings with OGS by relative K and V of ground and adjacent upper storey. Quantifying design criteria for such structural configurations based on Design Amplification Factor (DAF) for ground storey columns is preferable. K and V of storey depends on masonry strength, central opening (OP) in infills and interaction between wall infill and frame. In the current study, DAF is proposed to overcome OGS effect considering the above parameters. Additional parameters like Stiffness factor (KF) and strength factor (VF), ratios of elastic lateral stiffness (KE) and maximum base shear (Vmax) of particular Strengthened OGS (SOGS) frame with respect to corresponding full infill (FI) frame is compared. DAF, KF and VF vary in the range of 2.5-6, 0.9-1 and 4-10, respectively, for a particular frame type. Obtained results indicate that the presence of infill affect the lateral load behaviour of OGS building.

Natural vibration period of buildings located at soft soil sites in Patna Avik Samanta, Mohd Zia Hussain

Natural vibration period is an important parameter in seismic design and response analysis of structures. This study focuses on the estimation of natural vibration period of RC buildings located on soft soil sites. In this study, natural vibration period of buildings are investigated using ambient vibration tests performed on 51 RC buildings at different parts of Patna, Bihar. Empirical relationships between the natural vibration period and height of residential buildings in Patna are proposed.

Evaluation of seismic resilience of a building with and without URM infill walls Prasanth S., Goutam Ghosh

In past years, the natural disaster has a serious impact over the human society which causes a loss of resilience of the structure because of the reduction in functionality and demands recovery of the structure. Therefore, it is of paramount important to determine the resilience of a structure at post-earthquake event to judge the remaining functionality. In this study, the seismic resilience of an unsymmetrical L-shaped reinforced concrete building has been evaluated. Both the bare frame and unreinforced masonry (URM) infill buildings have been considered in the study. The result shows that with URM infills, the resilience of the building goes down below 70% due to significant loss in the functionality of the building which is useful from designer point of view for strategic planning. Based on this, the possibility of recovery with optimum time and cost can be planned.

Constructability and Detailing of RC Coupling Beams N. Subramanian

Coupled shear walls of multi-storey reinforced concrete buildings have been used in the past in earthquake zones. However, conventionally reinforced concrete coupling beams with length to depth ratio less than 4.0 were found to have deficient performance, especially during earthquake loading. Based on extensive experimental research, researchers have found that detailing of coupling beams using inclined reinforcement are more effective and perform better with adequate ductility. But such a detailing resulted in two constructability problems: (1) Two groups of diagonal reinforcement have to be provided with closely spaced ties, and (2) These diagonal bars have to be anchored in the adjacent walls, with 1.5 times the development length. ACI 318 (2019) suggested an alternate detailing option, where transverse reinforcement is placed around the beam cross section to provide confinement and suppress buckling, and no transverse reinforcement directly around the diagonal bar bundles. Such an option should also be provided in IS: 13920 (2016) for easy constructability. Various other alternate reinforcement details involving diagonal reinforcement, which are bent at the beam ends inside the coupling beam have also been proposed. The use of HPFRC with low volume fractions of fibres, can not only reduce the amount of steel used, but also reduce labour by simplifying the placement of reinforcement and accelerate construction schedule of these coupling beams.

Dynamic characteristics and seismic behavior of plan irregular buildings Pranab Kumar Das, Sekhar Chandra Dutta

The present study is an effort to investigate the reason of severe seismic vulnerability of structures with plan irregularity. Such structures are found very commonly all over the world. This study initially aims to model the structures in standard finite analysis based software maintaining their accurate geometrical shape find out natural mode shapes and natural lateral periods of such systems. Closeness between higher and lower lateral periods indicate the reasonable possibilities of influence of higher modes in overall seismic response. The higher modes are seen to have concentrated deformations at some critical locations. To understand the implication of this observation, further, a response spectrum based CQC (complete quadratic combination) analyses are carried out. Outcome exhibits that the similar critical locations are over stressed. The early yielding in these locations may result in load transfer to other members subsequently. Such cascading effect is predicted as the possible reason of increased vulnerabilities of such structures. Relatively, more strengthening of such members in critical zones may help to alleviate these problems. Alternatively, the building may be structurally divided into rectangular blocks so that they can undergo independent vibration eliminating the possibility of stress concentration. Further, detailed study encompassing many possible irregular plan building is the need of the hour for formation of design provisions.

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