The existing practice to estimate seismic performance of a regular building is to carry out nonlinear time history analysis using two-dimensional models subjected to unidirectional excitations, even ...though the multiple components of ground motion can affect the seismic response, significantly. During seismic shaking, columns are invariably subjected to bending in two orthogonal vertical planes, which leads to a complex interaction of axial force with the biaxial bending moments. This article compares the seismic performance of regular and symmetric RC moment frame buildings for unidirectional and bidirectional ground motions. The buildings are designed and detailed according to the Indian codes, which are at par with the other modern seismic codes. A fiber-hinge model, duly calibrated with the biaxial experimental results, is utilized to simulate the inelastic behavior of columns under bidirectional bending. A comparison of the estimated seismic collapse capacity is presented, illustrating the importance of considering the bidirectional effects. The results from fragility analysis indicate that the failure probabilities of buildings under the bidirectional excitation are significantly higher as compared to those obtained under the unidirectional excitation.
The seismic performance of existing RC frame buildings seismically retrofitted by base isolation is examined. Two different types of isolation systems are considered, i.e.: rubber-based and ...friction-based isolation systems, respectively. Two different performance levels are examined, namely: Global collapse prevention and Usability preventing damage. Seismic performance is assessed by multi-stripe nonlinear time-history analysis, considering earthquake intensity levels with return period ranging from 10 to 100000 years. Results point out that seismic isolation works effectively in limiting damage well beyond the design limit state level while it shows a limited margin with respect to collapse beyond the design limit state level.
The downtime due to earthquake damage in RC buildings is examined. The rational component of downtime is evaluated based on the results of probabilistic seismic loss assessment analyses, using ...suitable time estimating manuals for civil construction works. The irrational component of downtime is derived from empirical data relevant to post-earthquake reconstruction in Italy. Suitable criteria are then adopted to monetize the downtime for indirect loss estimation. Finally, a simplified model, expressing indirect monetary loss as a function of the earthquake intensity level, is tentatively proposed, to be incorporated in practice-oriented procedures for the estimation of the expected annual loss of residential RC buildings.
•The downtime of RC buildings due to earthquake damage is examined.•The rational and irrational components of downtime are evaluated.•Downtime is monetized based on rational criteria for residential buildings.•A simplified indirect loss vs earthquake intensity measure model is proposed.•The study emphasize the importance of indirect losses compared to direct losses.
Openings provided to meet functional requirements are often neglected in analytical assessment of Un-Reinforced Masonry (URM) infilled Reinforced Concrete (RC) frame buildings, mostly due to ...unavailability of simplified comprehensive model to simulate its effect. Ignoring presence of opening in infills results unrealistic assessment of seismic response for these popular building typologies, as opening reduces the strength and stiffness of the composite frame. Several reduction factor models have been developed over the years to account effect of opening in infills. In the present study efficacy of five such models of opening have been investigated which can be used by design practitioners for simulation of opening with sufficient accuracy in predicting the response of composite frame. Extensive analytical study has been conducted on a set of mid-rise and high-rise Indian infilled RC frame buildings considering various realistic combinations of openings by varying size, shape of doors and windows. The study revealed that increasing opening in infills significantly affects the seismic performance, and consequent fragility thereby reduces lateral strength, stiffness, ductility, while increasing fundamental time period, overall deformation capacity and damage probability.
•Effect of the presence of URM infills on floor acceleration demand is studied.•Correlation of floor spectra with PGA, PFA and ground response spectrum is studied.•Model for construction of floor ...spectra directly from ground spectrum is developed.•Computation of floor spectra for a targeted ductility demand in supporting structure.
The effect of unreinforced masonry infills on the floor acceleration response of inelastically responding mid-rise RC frame buildings is studied using incremental dynamic analyses. Two structural building configurations, uniformly infilled, and with open ground storey are analyzed by using the FEMA P695 far-field ground-motion suite. It is observed that the effect of structural nonlinearity is much more pronounced in case of infilled RC frame buildings than bare RC frame buildings. Sequential failure of infills results in a significant elongation of period of vibration resulting in the shifting of peaks in floor spectrum towards longer periods. Modified floor spectral amplification functions are presented for both uniformly infilled and open ground storey RC frame buildings. The proposed spectral amplification functions are validated using nonlinear analysis of typical buildings for recorded as well as spectrum-compatible ground-motions and can be used to estimate the floor response spectra directly from the code-based or site-specific design spectra.
Past earthquakes have shown that seismic events may incur large economic losses in buildings. FEMA P-58 provides engineers a practical tool for the performance seismic assessment of buildings. In ...this article, FEMA P-58 is applied to a typical Italian pre-1970 reinforced concrete frame building, characterized by plain rebars as steel reinforcement and masonry infills and partitions. Given that suitable tools for these buildings are missing in FEMA P-58, in the first part of the article, specific fragility curves and loss functions for the main structural and non-structural components of the building type under consideration are proposed. In the second part, building performance is evaluated following a time-based assessment approach. Expected economic losses in form of repair costs are then derived. Finally, results are compared with those from past applications to old RC frame buildings.
Irregular reinforced concrete (RC) buildings constitute a significant portion of the existing housing stock. A common type of irregularity is in the form of discontinuity in the vertical framing ...elements, which can exacerbate their seismic vulnerability. The design guidelines available in seismic design codes essentially cater to only regular buildings, and the safety of such buildings, even when the other guidelines of the codes are followed, is doubtful. This article evaluates the vulnerability of RC frame buildings with discontinuity in columns designed for modern seismic codes, in the form of seismic collapse capacity, collapse resistance against maximum earthquake demand level, and failure mechanism. The adequacy and limitations of the provisions of the seismic design codes are evaluated for such buildings. Analysis results show that the sequential analysis of buildings considering the construction staged effects, considerably affects the design and hence the collapse failure mechanism of even low‐ and mid‐rise buildings. The results also underline the importance of strong column–weak beam design in the seismic performance of the floating column buildings. The vertical component of ground motion is also observed to be relatively more crucial in floating column buildings.
Past earthquakes have repeatedly shown that damage to masonry infills can produce large economic losses and even jeopardize human lives. Nevertheless, in current design practice masonry infills are ...ignored, while available macro-models for nonlinear analysis focus the attention on the In-Plane (IP) behavior of masonry infills only, while neglecting the Out-Of-Plane (OOP) collapse mechanism. The main objective of this study is to investigate the seismic performance of RC frame buildings accounting for the interaction between IP and OOP behavior of masonry infills. To this end, a suitable nonlinear model, able to capture the IP stiffness and strength reduction due to the OOP displacement demand (and vice versa) is implemented. The selected model incorporates a routine that removes infills from the structural model when either IP or OOP collapse occurs. Different building models, representative of typical residential buildings, realized in Italy (and other European countries) from 50’s to 90’s, are examined through nonlinear response-time history analysis at different earthquake intensity levels, with return period ranging from 30 to 5000 years. Two alternative infill configurations (single layer and double layer with inner cavity) are considered, in accordance with the construction practice of the time. The comparison between the models with and without IP/OOP interaction points out the relevance of the OOP behavior towards an accurate evaluation of the seismic performance of RC frame buildings. A set of fragility curves is tentatively proposed, for different building performance levels, ranging from immediate occupancy to life safety.
In Nepal, the reinforced concrete (RC) frame system is commonly used to construct low-rise buildings. In last three decades, a significant number of such buildings were proportioned and constructed ...in accordance with Nepal National Building Code NBC 205:1994 and NBC 205:2012—also known as the Mandatory Rule of Thumb (MRT). In the aftermath of 2015 Gorkha Earthquake (Mw 7.8) which resulted in large scale social and economic losses, the efforts to formulate improved seismic design provisions led to the development of NBC 105:2020. Considering that MRT-designed low-rise RC frame buildings still constitute a significant part of existing building stock, this study is aimed to conduct a comparative seismic performance evaluation of several case study structures under a comprehensive set of ground motions. Using the nonlinear analysis and seismic fragility assessment of four low-rise RC frame buildings (designed using all three code versions), it is shown that the structural performance and seismic losses can be significantly reduced by following NBC 105:2020 provisions. Several retrofitting solutions are also explored to improve the seismic performance of buildings designed using MRT. It is shown that the concrete or steel jacketing of RC columns can significantly increase the lateral strength and energy dissipation, and reduce the damage probability of such buildings. Lastly, based on the developed results, a machine learning approach is employed to correlate the peak ground acceleration with structural drifts for convenient practical applications.
•Different representative building typologies were developed based on simplified code of practice in Nepal.•Incremental dynamic analysis (IDA) was carried out for development of frazility curves.•Different retrofitted techniques were studied and suitable method was suggested to strengthen low-rise building typologies of Nepal.•Ground motion parameter and their effect on structural response (Inter storey drift) were evaluated using machine learning (ML) techniquies.
Effect of different proportioning of lateral force-resisting system in the orthogonal directions, on seismic collapse capacity and fragility of reinforced concrete buildings is investigated. ...Buildings with different structural systems and configurations, are designed for a modern seismic design code. To simulate the structural collapse, the hysteretic models of beams, columns, and shear walls are duly calibrated using experimental tests results. Results show that if the buildings of a given height are designed for the same hazard level, these show equal levels of safety against collapse, irrespective of the proportioning of lateral load resisting systems in the orthogonal directions.
PDF