Reflection of the seismic vulnerability associated to common RC buildings in Nepal

Engineering Structures, 2012

This paper presents the seismic response of the current reinforced concrete (RC) buildings in Nepal. It was achieved by non-linear static and dynamic analyses of four structures corresponding to four scenarios of design/construction, namely a building: (i) representing the Current Construction Practice (CCP) (ii) the Nepal Building Code (NBC), (iii) the Modified Nepal Building Code (NBC+) and (iv) a Well Designed Structure (WDS). The seismic demands are analyzed and discussed in terms of base shear, maximum roof displacement, capacity curve and inter-storey drift. The results indicate a good correlation between the static and dynamic methods. The Current Construction Practice (CCP) structure and Nepal Building Code (NBC) structures experience inter-storey drift demands higher than the other models and they also present some irregularities in the drift profile. The modified Nepal Building Code (NBC+) and Well Designed Structure (WDS) have presented a better performance with low inter-storey drifts. Finally, the safety assessment is performed based on drift limit proposed by ATC-40 and FEMA-356, showing that CCP and NBC building are highly vulnerable to earthquakes.

2015

RC buildings constitute the prevailing type of construction in earthquake-prone region like Kathmandu Valley. Most of these building constructions were based on conventional methods. In this context, the present paper studied the seismic behaviour of existing RC buildings in Kathmandu Valley. For this, four representative building structures with different design and construction, namely a building: (a) representing the non-engineered construction (RC1 and RC2) and (b) engineered construction (RC3 and RC4) has been selected for analysis. The dynamic properties of the case study building models are analyzed and the corresponding interaction with seismic action is studied by means of non-linear analyses. The structural response measures such as capacity curve, inter-storey drift and the effect of geometric nonlinearities are evaluated for the two orthogonal directions. The effect of plan and vertical irregularity on the performance of the structures was studied by comparing the results of two engineered buildings. This was achieved through non-linear dynamic analysis with a synthetic earthquake subjected to X, Y and 45° loading directions. The nature of the capacity curve represents the strong impact of the P-delta effect, leading to a reduction of the global lateral stiffness and reducing the strength of the structure. The non-engineered structures experience inter-storey drift demands higher than the engineered building models. Moreover, these buildings have very low lateral resistant, lesser the stiffness and limited ductility. Finally, a seismic safety assessment is performed based on the proposed drift limits. Result indicates that most of the existing buildings in Nepal exhibit inadequate seismic performance.

2016

On April 25 a devastating 7.8 Mw shallow earthquake struck Nepal, causing over 9000 deaths and almost 23000 injuries. More than 400 aftershocks, with magnitude larger higher than 4.0Mw, occurred in the following two months. The earthquake and the aftershocks caused a significant number of damaged and collapsed buildings. In this context the present manuscript pretends to be an overview of the buildings damages observed over the course of 10-days reconnaissance trip that took place 2 months after the earthquake. A general summary of the tectonic region and seismicity characteristics will be provided as well as the reinforced concrete (RC) buildings will be characterized in terms of typologies, and more detailing aspects, with and overview of the constructive practices adopted in Nepal and of the current standards and codes. The structural performance of the RC buildings during the seismic events, particularly the influence of the masonry infill walls in the structural response will b...

Structural Engineering and Mechanics, 2015

RC buildings constitute the prevailing type of construction in earthquake-prone region like Kathmandu Valley. Most of these building constructions were based on conventional methods. In this context, the present paper studied the seismic behaviour of existing RC buildings in Kathmandu Valley. For this, four representative building structures with different design and construction, namely a building: (a) representing the non-engineered construction (RC1 and RC2) and (b) engineered construction (RC3 and RC4) has been selected for analysis. The dynamic properties of the case study building models are analyzed and the corresponding interaction with seismic action is studied by means of non-linear analyses. The structural response measures such as capacity curve, inter-storey drift and the effect of geometric nonlinearities are evaluated for the two orthogonal directions. The effect of plan and vertical irregularity on the performance of the structures was studied by comparing the results of two engineered buildings. This was achieved through non-linear dynamic analysis with a synthetic earthquake subjected to X, Y and 45° loading directions. The nature of the capacity curve represents the strong impact of the P-delta effect, leading to a reduction of the global lateral stiffness and reducing the strength of the structure. The non-engineered structures experience inter-storey drift demands higher than the engineered building models. Moreover, these buildings have very low lateral resistant, lesser the stiffness and limited ductility. Finally, a seismic safety assessment is performed based on the proposed drift limits. Result indicates that most of the existing buildings in Nepal exhibit inadequate seismic performance.

Earthquakes occurred in recent past around the world have indicated that if the structures are not analyzed and designed with adequate requirements may cause a great destruction of structures apparently resulting in human as well as financial losses. Hence, going for the study of buildings with broad and expanded considerations are needed to decide the further precautionary measures for the designers in future. In this study is the 10 storey building damaged in Nepal earthquake on 25th April, 2015.The paper was published named, "Performance of a ten story reinforced building damaged in the 2015 Nepal Gorkha Earthquake" and the resistance of the building to the seismic demands was found inadequate. The analysis of the building model is again done with the adoption of different known time histories from the past and the comparative study was carried out on the model using the same response history analysis and inverted triangular based pushover analysis. The failure criterio...

2018

Kathmandu city core, one of the densest settlement area of Nepal, has its own cultural, historic, religious as well as commercial significance and consists of various structures from masonry to RC frames. The structures in the Kathmandu city core are unique. Construction of large structures within the limited area has resulted in construction of many seismically deficient structures. The dense settlement and thick layer of underlying soft soil make structures within the Kathmandu city core more vulnerable to earthquake. This research thus deals with finding the seismic vulnerability of RC frame buildings within the city core in terms of fragility curves. This research also focuses on comparison of the losses estimated by various researchers adopting various methodology to the actual losses that occurred in RC frame buildings of Kathmandu city core due to the Gorkha earthquake of 2015.

This paper will present a case study on Seismic performance evaluation and enhancement of RC structures like building bridge etc. A case analysis will be carried out for numbers of seismic vulnerable structures, from a developing country like Nepal. Linear static analysis, nonlinear static (pushover analysis) and nonlinear dynamic analysis (time history analysis) using the displacement coefficient method, as described in FEMA 356, will be used to evaluate the seismic performance of the structure models. This case study provides a unique and intriguing investigation of seismic performance evaluation and help in performance enhancement of the structural member with the retrofit techniques for the developing countries.

Advances in Structural Engineering, 2014

The present paper analyses the design procedure and its impact on seismic safety of the structures. For this, a representative reinforced concrete frame building (WDS) is designed and the results are compared with similar buildings detailed with: i) Current Construction Practices (CCP); ii) the Nepal Building Code (NBC) and iii) the Modified Nepal Building Code (NBC+) recommendations. The seismic performance evaluation is done with global strength, inter-storey drift and displacement of the structures. Likewise, the sensitivity of the structural and geometrical parameters of the RC frame building is studied through nonlinear analysis. The study parameters considered for parametric analysis are column size, beam size, inter-storey height, bay length, bay width, and compressive strength of concrete. The results show that the influence on the structural behaviour, particularly by variation in column size and inter-storey height. Additionally, the influence of the seismic zone factor on...

Cinpar 2013 (Conference paper), 2013

The effectiveness of reinforced concrete (RC) column jacketing for improving the seismic performance of existing RC building structures were studied. Four three storey buildings with different structural configuration and detailing were selected for seismic assessment and retrofitting purpose. The response of structures (original and retrofitted) was evaluated in terms of capacity curve and inter-storey drift. The case studies also intend to verify the effect of P-delta effects and bi-axial response of columns under non-linear time history analysis. The nature of the capacity curve represents the strong impact of the P-delta effect, leading to a reduction of the global lateral stiffness and reducing the strength of the structure. Finally, a seismic safety assessment is performed based on the drift limit proposed by FEMA-356. The assessment of original building structures indicates that they may exhibit inadequate seismic performance. However, RC column jacketing highly improves seismic performance of all the structures and results maximum drift demand within the drift limit proposed by FEMA-356.