Seismic performance evaluation and risk assessment of typical reinforced concrete frame buildings with masonry infill and conventional vertical extension in Nepal

Many reinforced concrete (RC) frame buildings in Nepal were significantly damaged by the 7.8 magnitude (Mw) earthquake in Nepal on April 25, 2015. To contribute to mitigate future earthquake disasters, the current study focuses on two specific characteristics of residential RC frame buildings in the capital city of Nepal, Kathmandu: the application of brick masonry infill to exterior and partition walls, and the conventional vertical extension of building stories different from the design. Although these factors are likely to significantly affect the seismic performance, their effects are frequently neglected in practical design and construction management in developing countries. Hence, the main objective of this research is to investigate and clarify the seismic performance of RC frame buildings considering the above factors through experimental and numerical investigations. The present paper (1) briefly introduces the characteristics of a typical residential RC frame building in Kathmandu, (2) illustrates the numerical modeling parametrically considering three different contributions of brick masonry infill walls and (3) investigates the seismic performance of the RC frame building considering the effects of the infill wall modeling and the vertical extension through numerical analyses. Consequently, it was found that the consideration of the in-plane stiffness and strength of the infill walls resulted in both positive and negative contributions to the seismic performance of low-rise (up to three stories) and medium-rise (more than three stories) buildings respectively, quantitatively clarifying significant effects of the presence of infill and the vertical extension. These findings contribute to provide realistic solutions to upgrade the seismic performance by utilizing or removing the brick masonry infill walls or by managing the building stories to mitigate future earthquake disasters on typical RC frame buildings not only in Nepal but also in other countries with similar backgrounds.

Requalification of RC Frame Apartment Buildings: Comparison of Seismic Retrofit Solutions Based on a Multi-Criteria Approach

Increasing environmental concerns are leading to measures and incentives aimed at reducing the energy consumption of buildings, which must be accompanied by substantial mitigation of seismic and structural risk. As for technical issues, it is important to select effective solutions specifically for medium-size RC apartment buildings (e.g., 3–6 storeys), which is where a large share of the Italian population lives today. To this end, it is important to compare, among other factors, the direct and indirect costs related to alternative techniques, thus allowing stakeholders (mainly private) and designers to select the most suitable solution for each case at hand and, finally, to speed up the design process. In this paper, different seismic strengthening techniques are designed and applied to a case study RC frame building that is representative of the EU building stock. An in-depth comparison is made with the aim of showing the advantages and disadvantages of different choices, mainly based on required costs and possible disruptions, keeping the targeted structural performance equal. Specifically, the possibility of disruption is a key point in hastening or, more frequently, hindering the implementation of the decision. In fact, people’s hesitation to leave their home, as well as the difficulty and high costs involved in finding temporary apartments if many people are involved, generally prevent such interventions from taking place. For this reason, some state-of-the-art techniques—that have minimum impact on non-structural elements, that can be applied only on the outside, and that can still provide an effective seismic retrofit—are examined and critically compared in the paper through a multi-criteria decision-making method.

Compliance-based estimation of seismic collapse risk of an existing reinforced concrete frame building

Seismic evaluation of existing structures is based on determining the damage likely to occur during the lifetime of these structures due to earthquake ground motion excitation. However, there is not a consensus about the acceptable level of seismic damage, the expected lifetime of these structures, and the seismic hazard level(s) to evaluate the structures at. This paper presents a methodology for a parametric calculation of the seismic collapse risk of an existing Reinforced Concrete (RC) frame building based on its seismic code compliance, quantified by a dimensionless metric. This metric, defined as compliance factor, compares the seismic capacity of an existing structure with the seismic demand for a new structure at a predetermined hazard level. The inelastic seismic behavior of four models of the RC frame building of varying compliance was analytically investigated in this study to demonstrate the novel methodology. The four models of the RC building were chosen to represent existing RC frame structures designed and constructed before the introduction of modern seismic code provisions. These four building models were excited by a group of earthquake ground motion excitations using Incremental Dynamic Analysis. The collapse probabilities of the four building models, representing varying values of seismic code compliance, were determined for two different locations corresponding to regions of moderate and high seismic hazard, thus laying the basis for the compliance-based estimation of the seismic collapse risk of existing structures.

Chinese High Rise Reinforced Concrete Building Retrofitted with CLT Panels

Cross laminated timber (CLT) panels have been gaining increasing attention in the construction field as a diaphragm in mid- to high-rise building projects. Moreover, in the last few years, due to their seismic performances, low environmental impact, ease of construction, etc., many research studies have been conducted about their use as infill walls in hybrid construction solutions. With more than a half of the megacities in the world located in seismic regions, there is an urgent need of new retrofitting methods that can improve the seismic behavior of the buildings, upgrading, at the same time, the architectural aspects while minimizing the environmental impact and costs associated with the common retrofit solutions. In this work, the seismic, energetic, and architectural rehabilitation of tall reinforced concrete (RC) buildings using CLT panels are investigated. An existing 110 m tall RC frame building located in Huizhou (China) was chosen as a case study. The first objective was to investigate the performances of the building through the non-linear static analysis (push-over analysis) used to define structural weaknesses with respect to earthquake actions. The architectural solution proposed for the building is the result of the combination between structural and architectonic needs: internal spaces and existing facades were re-designed in order to improve not only the seismic performances but also energy efficiency, quality of the air, natural lighting, etc. A full explanation of the FEM modeling of the cross laminated timber panels is reported in the following. Non-linear FEM models of connections and different wall configurations were validated through a comparison with available lab tests, and finally, a real application on the existing 3D building was discussed.

Effect of uniform temperature load on design of long reinforced concrete structures without expansion joints

This study presents an investigation on the design of long reinforced concrete (RC) structures subjected to uniform temperature load by considering three RC frame building models with different lengths of 45 m, 135 m, and 270 m using Etabs. The uniform temperature load is considered being the change from the annual average highest to lowest air temperature at the construction site in the case of unavailable temperature data of concrete. The analysis results indicate that the uniform temperature load mainly influences on the internal forces of RC members at storey 1 and slightly effects on the internal forces of RC members at storey 2. For short-length RC structures, the effect of temperature load can be ignored in the design of RC elements, whereas it must be taken into account in design of slab, beams and some column positions at storey 1 of medium-length and long RC structures without expansion joints. For the present RC frame building models, the required slab reinforcement in long direction increases about 33.4% for medium-length RC structures (135 m) and about 48.2% for long RC structures (270 m) without expansion joints. The required reinforcement for positive moment at mid-span increases from 33.7 to 39.4%, whereas the total required reinforcement for negative moment at the supports of beams increases from 19.4 to 34.9% in long direction of 270 m long RC structures without expansion joints due to uniform temperature load. Column design of long RC structures without expansion joints under uniform temperature load must be concerned, especially for columns in the corners.

Seismic Performance of Multistorey RC Frame Building With The Soft Storey and Masonry Infill

In this study, four geometrically similar frames having different configurations of masonry infills, has been investigated. In this article attempts are made to explain the factors that impact the soft storey failure in a building are compared with different type of infill. That is Four models like RC bare frame, RC frame with brick mansonry infill, RC frame with brick infill in all the storeys exept the firstsoft storey, RC frame with inverted V bracing in the soft storey. Time history analysis has been carried out for a G+8 multistoried building to study the soft storey effect at different floor levels using E tabs software. The behavior of RC framed building with soft storey under seismic loading has been observed in terms of maximum displacement ,maximum storey drift, base shear and storey stiffness as considered structure.