Reinforced Concrete Frame Buildings Research Articles

Investigation on improving the shear behavior of columns in masonry infilled RC frames under lateral loads

Presence of infills in reinforced concrete (RC) frames enhances the lateral load behavior of the bare frame system, but makes the columns vulnerable to shear failure under strong ground motions. This local adverse effect of infill is more pronounced in exterior ground storey columns where strong and stiff infills are present on one-side of the columns. Some of the current seismic standards address the local adverse effect of infill using variety of recommendations but their application is limited. Therefore, it is of primary importance to develop methods to counteract the adverse effect of infill. To prevent or delay the shear failure of columns, three methods (increasing the dimensions of the columns taking care of the effect of infill, using weak and soft masonry to reduce the effect of infill on columns, and decreasing the frame-interaction using collector beams in infills) were adopted in the present experimental study. From the results, it was observed that the methods not only enhanced the lateral load behavior, but also delayed the shear failure of columns without compromising the other functional requirements. The three methods can be efficiently used in both existing and new constructions to reduce the seismic vulnerability of masonry infilled RC frame buildings.

Seismic behavior of masonry-infilled precast concrete frames considering effects of opening

Abstract It is commonly accepted that addition of infilled masonry walls (IMW) could enhance the in-plane strength and stiffness of RC frame buildings subjected to seismic loads. However, once the IMW walls failed, the shear force initially resisted by the IMW has to be transferred to the surrounding frames and may incur shear failure to the frames. Despite the extensive studies carried out in the past decades, studies on the structural performance of masonry infilled precast concrete (PC) frames are few. In this study, eight half-scaled single-story one bay frame were tested subjected to seismic loading, including three reinforced concrete (RC) frames and five PC frames. The investigated PC frames deviates the beam potential plastic hinge zone away from beam-to-beam connection region. The variables investigated in the tests included the types of opening in masonry infill walls and the types of cast-in-place concrete at the connections (normal concrete or steel fiber reinforced concrete). Results indicated that the investigated PC construction method has minimal effects on inelastic behavior and ductility of bare and infilled frames. However, the PC construction method may affect the crack development, especially at the interfaces in between precast and cast-in-place concrete surfaces in the region of the connection. However, the load resisting capacity and ductility was insensitive to the usage of steel fiber reinforced concrete at the connections, especially for bare frames.

Incorporation of Torsional & Higher-Mode Responses in Displacement-Based Seismic Design of Asymmetric RC Frame Buildings

Direct displacement-based design (DDBD) is currently a widely used displacement-based seismic design method. DDBD accounts for the torsional response of reinforced concrete (RC) frame buildings by using semi-empirical equations formulated for wall-type buildings. Higher-mode responses are incorporated by using equations obtained from only a few parametric studies of regular planar frames. In this paper, there is an attempt to eliminate torsional responses by proportioning frames’ secant stiffnesses so that the centers of rigidity and supported mass (the mass on and above each story) coincide. Once the torsional rotations are significantly reduced and only translational motions are achieved, higher-mode responses are included using a technique developed by the authors in their recent paper. The efficiency of the proposed design procedure in fulfilling the intended performance objective is checked by two plan-asymmetric 20-story RC frame building cases. Case-I has the same-plan configuration while Case-II has a different-plan configuration along the height. Both cases have different bay widths in orthogonal directions. Verification of the case studies by nonlinear time history analysis (NTHA) has shown that the proposed method results in designs that satisfy the performance objective with reasonable accuracy without redesigning members. It is believed that a step forward is undertaken toward rendering design verification by NTHA less necessary, thereby saving computational resources and effort.

Robustness of RC buildings to progressive collapse: Influence of building height

The influence of building height on the robustness of reinforced concrete (RC) frame buildings to resist progressive collapse is investigated. Beginning with the initial removal of a corner column at the ground level, the study attempts to identify the main global resisting mechanisms that develop in the structure after successive column removals and provides an assessment of the building robustness with varying height. Nonlinear simulation models of three, six and ten-story RC frame buildings using reduced-order modeling scheme were developed in LS-DYNA and the results were analyzed to gain insight into the factors that influence the ability of the structure to accommodate vertical load redistribution, develop arch and catenary action, and trigger Vierendeel effects. It is observed that taller buildings possess greater resilience to progressive collapse than buildings with fewer stories for the same arrangement of vertical elements in the building plan, although a comprehensive analysis of the failure modes also indicates that this finding cannot be extrapolated to conclude that collapse resistance will continue to increase with increasing buildings height. The research provides a basis for comparing the relative robustness of buildings subjected to column losses on the lowest floor and, consequently, findings from the study provide engineers with an insight into measures to improve the robustness of a building to resist progressive collapse.

Seismic Performance of a New Structural Design Solution for First-Story Isolated RC Buildings with Coupled Beam-Column Connections

This study proposes a new structural design of the first-story isolation system in reinforced concrete (RC) structures. Compared to the conditional buildings with independent columns, this new design integrates the independent columns with beams to increase the seismic capacity of the building by increasing the integrated stiffness of the coupled columns and the stability of the isolation system. The seismic responses of the proposed structure and the corresponding isolation effect were investigated by performing a series of numerical simulation and shaking table tests on a typical 7-story RC frame structure. The structure models were subjected to four earthquake waves with two PGAs (peak ground acceleration) of 0.30 g and 0.40 g for seismic analysis regarding the peak acceleration and inter-story displacement. Both simulation and testing results showed that the story acceleration and inter-story displacement of the superstructure in the isolated model decreased significantly. While the substructure below the isolation layer had a negligible decrease of acceleration. The connection of beams with concrete columns significantly increases the seismic capacity of the RC frame buildings compared to non-isolated frame buildings. The coupled beam-column connections could thus be potentially adopted in the practical first-story isolation system to avoid the requirements of large column stiffness and large column size.

Accounting for Torsional Response in Direct Displacement-based Design of Plan-asymmetric Reinforced Concrete Frame Buildings

The torsional response of Reinforced Concrete (RC) frame buildings within the Direct Displacement-Based Design (DDBD) framework is considered by using semi-empirical equations developed for wall-type asymmetric structures. These equations when applied to RC frame buildings result in the underestimation of engineering demand parameters such as drifts. To alleviate this problem, it is proposed that first-mode effective masses of the frames are connected with rigid bar, constraining the system so that the critical frames’ design displacements are not exceeded and displacement compatibility for all frames is maintained. The proposed method of seismic design is verified by a Nonlinear Time History Analysis (NTHA) of two six-story plan-asymmetric RC frame buildings, the only difference in the buildings being that one is applied with equal mass and the other variable mass along the height. Eleven ground motions are selected and scaled to match a design response spectrum of a given seismic hazard level at the building site. The proposed design procedure produces reasonable response outputs when verified by NTHA of the case studies. Thus, it is a step toward minimizing the use of NTHA for plan-asymmetric frame buildings, thereby saving computational resources and effort.

Numerical Evaluation of Seismic Response of Asymmetrical Reinforced Concrete Frame Buildings

Asymmetrical multi-storey buildings are almost unavoidable in modern structures due to various types of useful and architectural requirements. Latest earthquakes showed that irregular distribution of mass, stiffness and strength cause serious damage in building structural systems. This paper investigates the numerical simulation of buildings with plan irregularity and presents a case study to demonstrate the numerical evaluation of the seismic response of a three real plan-asymmetric reinforced concrete building tested at full scale at the European Laboratory for Structural Assessment of the Joint Research Center, Ispra / Italy within the SPEAR project. The structural evaluation performed through a validated Finite Elements Package, modeled by the general purpose ABAQUS, which is able to run accurate analysis, in particular nonlinear static and dynamic analysis considering both geometric nonlinearity and material inelasticity.Adequacy of the numerical modeling is verified by comparing numerical and experimental results through evaluation of the seismic capacity and dynamic characteristics of the building. The provisions of the adopted seismic code for designing such buildings are also checked over and done with the nonlinear static and dynamic analysis by verifying the proficiency of an analytical model for simulating the nonlinear response of structures considered to conduct an investigation into experiments.

Optimization Approach to Flat Slab Reinforced Concrete Building Frame Design

Optimization Approach to Flat Slab Reinforced Concrete Building Frame Design

Financial risk evaluation of non-ductile reinforced concrete buildings in eastern and western Canada

Financial risks due to catastrophic earthquakes can be severe. This is particularly applicable to existing buildings that were constructed prior to modern seismic hazard maps and seismic design provisions. Pre-1970 non-ductile reinforced concrete (RC) frame buildings in Canada are of typical examples, where design base shear coefficients were essentially the same across the country, despite very diverse seismic hazards in the east and the west. This study implements a comprehensive performance-based earthquake engineering methodology to evaluate the financial risks of non-ductile RC frame buildings with different numbers of stories for seismicity in Montreal and Victoria. In addition to seismic loss curves that consider a comprehensive event set of regional seismicity, conditional loss distributions for critical scenarios are developed. The results of the financial risk evaluations for the buildings strongly indicate the effects of regional seismicity are significant and overall seismic risks for buildings in Victoria are greater than those in Montreal. Nevertheless, seismic vulnerability of these buildings remains to be high for both locations, meaning that should a major earthquake strike near the location, the buildings studied will suffer major damage. The results from the detailed risk assessments are also useful for developing effective financial risk mitigation strategies through earthquake insurance.

Seismic Risk Mitigation for a Portfolio of Reinforced Concrete Frame Buildings through Optimal Allocation of a Limited Budget

The mitigation of seismic risk for a population of vulnerable civil critical structures (e.g., hospitals, schools, and bridges) is a crucial issue for many governments of earthquake-prone regions. Furthermore, owing to the global economic crisis, limited financial resources make full seismic rehabilitation of entire building stocks challenging. Therefore, a critical decision has to be made on the following key question: what is the most advantageous way of spending the available budget while treating each building in a portfolio differently, by giving it a different level of structural improvement to reduce the overall risk of the portfolio of buildings as much as possible? Herein, a decision-making tool is proposed to address this high-social-impact issue. Starting with a limited amount of information, which is gathered through expeditious surveys on existing buildings, and by involving uncertainties, the overall risk is evaluated from the fragility analysis of each structure. This is conducted via simplified pushover analyses by considering the local seismic hazard. Then, an optimization is performed for each building of the portfolio to select a relevant structural intervention from four alternatives (no intervention, partial retrofit, full retrofit, and demolition and reconstruction), based on both the overall risk reduction and the amount of financial resources. Procedures for quick estimation of fragility curves and installation costs are also discussed as part of the proposed approach. Finally, a practical application is presented with reference to a simulated case study consisting of 46 reinforced concrete school buildings located in Campania, Italy.

Seismic response of autoclaved aerated concrete masonry infill walls under in‐plane and out‐of‐plane seismic demands

AbstractInfill walls of reinforced concrete (RC) frames exhibit significant vulnerability when subjected to in‐plane (IP) and out‐of‐plane (OOP) seismic demands. Despite the vast number of tests investigating the behavior of brick masonry infill walls in RC frames, past research is concerned with infill walls made up of autoclaved aerated concrete (AAC) blocks. In this study, six single‐bay, single‐story, half‐scaled RC frames were tested under the action of IP cyclic displacement excursions and/or OOP pressure. The objectives of the tests were to investigate the IP behavior of AAC infilled RC frames constructed with or without fiber mesh reinforced plaster to observe the influence of the OOP loads on the IP deformation capacity. It was found that AAC infill walls increased the strength and stiffness of the test frames compared to the bare frame specimen. The specimens without the plaster overlay experienced cracking at inter‐story drift ratio of about 0.35%. The ultimate drift ratio corresponding to a 20% lateral strength loss occurred at about 2% interstory drift ratio. The presence of plaster, on the other hand, delayed the visual cracking of the walls up until 1% interstory drift ratio. The OOP loads applied on the frame by using an airbag system was found to significantly reduce the IP deformation capacity of AAC framed infill walls. These results show that AAC infill walls may not sustain the IP and OOP seismic demands expected in RC frame buildings and innovative solutions are needed to limit the damage.

Savings in Consumption of Concrete and Steel and in the Related Cost of Various Reinforced Concrete Frame Buildings with Shear Walls Due to Implementation of Base Isolation Strategy

Savings in Consumption of Concrete and Steel and in the Related Cost of Various Reinforced Concrete Frame Buildings with Shear Walls Due to Implementation of Base Isolation Strategy

Application of an in-plane/out-of-plane interaction model for URM infill walls to dynamic seismic analysis of RC frame buildings

Experimental tests have shown that unreinforced masonry (URM) infill walls are affected by simultaneous loading in their in-plane and out-of-plane directions, but there have been few attempts to represent this interaction in nonlinear time history analysis of reinforced concrete (RC) buildings with URM infill walls. In this paper, a recently proposed macro-model that accounts for this interaction is applied to the seismic analysis of RC framed structures with URM infill walls representative of Mediterranean building stock and practices. Two RC framed structures that are representative of low and mid-rise residential buildings are analysed with a suite of a bidirectional ground motions, scaled to three different intensities. During the analyses, the in-plane/out-of-plane interaction is monitored, showing that cracking of the infills occurs predominantly by in-plane actions, while failure occurs due to a combination of in-plane and out-of-plane displacements, with the out-of-plane component usually playing the dominant role. Along the frame height, the bottom storeys are generally the most damaged, especially where thin infill walls are used. These results are consistent with observations of damage to URM infill walls in similar buildings during recent earthquakes.

Extension of Direct Displacement-Based Design to Include Higher-Mode Effects in Planar Reinforced Concrete Frame Buildings

Now that problems with force-based seismic design have been clearly identified, design is inclined toward displacement-based methods. One such widely used method is Direct-Displacement-Based Design (DDBD). Yet, one of the shortcomings of DDBD is considering higher-mode amplification of story shear, moments, and displacements using equations obtained from limited parametric studies of regular planar frames. In this paper, a different approach to account for higher-mode effects is proposed. This approach determines the lateral secant stiffness of the building frames that fulfill the allowable inter-story drift without exceeding the desired story displacements. Using the stiffness, an elastic response spectrum analysis is carried out to determine elastic higher-mode force effects. These force effects are then combined with DDBD-obtained first-mode force effects using the appropriate modal superposition method so that design can be performed. The proposed design procedure is verified using Nonlinear Time History Analysis (NTHA) of twelve planar frames in four categories accounting for mass and stiffness irregularity along the height. In general, the NTHA response outputs compared well with the allowable limits of the performance objective. Thus, it fulfills the aim of minimizing the use of NTHA for planar frame buildings, thereby saving computational resources and effort.

Experimental Studies on Fibre Integrated Lightweight Concrete Frames Under Lateral Forces: A Review

Reinforced Concrete (RC) framed structure with masonry infill is the most common type of building in which, RC frames participate in resisting lateral forces. The poor performance of RC frame buildings under lateral forces is due to its heavy mass and rigid construction. Use of Lightweight concrete (LWC) is preferred since the dead load of concrete is enormous. A low density of the LWC, decreases the weight of the building thus reducing the effect of lateral forces. However, LWC having a lower modulus of elasticity, has a faster rate of crack development in RC members. So, fibres are employed as an additive to increase the energy absorption capacity and to control the crack development. Pumice is a natural material of volcanic origin, has low density, which makes it ideal for production of LWC. Based on these ideas, Pumice aggregate is used as a partial replacement of coarse aggregate to its volume with addition of steel fibres to the volume of concrete. This paper summarizes the collected literatures related to RC frames, LWC, Fibre Reinforced Concrete (FRC) and thereby attempts to predict the lateral load response of RC portal frame with the use of LWC and Steel fibres.

Automated optimization of steel reinforcement in RC building frames using building information modeling and hybrid genetic algorithm

Abstract Design of steel reinforcement is an important and necessary task for designing reinforced concrete (RC) building structures. Currently, steel reinforcement design is performed manually or semi-automatically using computer software such as ETABS, with reference to building codes. These approaches are time consuming and sometimes error-prone. Recent advances in building information modeling (BIM) technology allow digital 3D BIM models to be leveraged for supporting different types of engineering analyses such as structural engineering design. With the aid of BIM technology, steel reinforcement design could be automated for fast, economical and error-free procedures. This paper presents a BIM-based framework using the developed three-stage hybrid genetic algorithm (GA) for automated optimization of steel reinforcement in RC frames. The methodology framework determines the selection and alignment of steel reinforcement bars in an RC building frame for the minimum steel reinforcement area, considering longitudinal tensile, longitudinal compressive and shear steel reinforcement. The first two stages optimize the longitudinal tensile and longitudinal compressive steel reinforcement while the third stage optimizes the shear steel reinforcement. International design code (BS8110) and buildability constraints are considered in the developed optimization framework. A BIM model in Industry Foundation Classes (IFC) is then automatically created to visualize the optimized steel reinforcement design results in 3D thereby facilitating design communication and generation of construction detailing drawings. A three-storey RC building frame is analyzed to check the applicability of the developed framework and its improvement over current design approaches. The results show that the developed methodology framework can minimize the steel reinforcement area quickly and accurately.

Safety Assessment of Gravity Load–Designed Reinforced Concrete–Framed Buildings

AbstractA large number of gravity load–designed (GLD) reinforced concrete (RC) buildings are found in many seismic-prone countries including India. Many of them were built before the advent of seis...

Assessment of Seismic Vulnerability of Reinforced Concrete Frame buildings

The seismic activity remains strong in the north of Algeria since no less than 30 earthquakes per month are recorded. The large number of structures built before the introduction of the seismic standards represents a high seismic risk. Analysis of damage suffered during the last earthquakes highlighted the vulnerability of the existing structures. In this study the seismic behavior of the existing buildings in Tizi-Ouzou city, located in the north of Algeria, is investigated. To make this assessment, a database was created following a building inventory based on a set of technical folders and field visits. The listed buildings have been classified into different typologies. Only reinforced concrete frame buildings are considered in this paper. The approach adopted to estimate structures damage is based on four main steps: 1) construction of capacity curves using static nonlinear method “push-over”, 2) estimate of seismic hazard, 3) determination of performance points, and finally 4) deduction of damage levels.

Structural robustness of RC frame buildings under threat-independent damage scenarios

This study focuses on a novel procedure for the robustness assessment of reinforced concrete (RC) framed structures under threat-independent damage scenarios. The procedure is derived from coupled dynamic and non-linear static analyses. Two robustness indicators are defined and the method is applied to two RC frame buildings. The first building was designed for gravity load and earthquake resistance in accordance with Eurocode 8. The second was designed according to the tie force (TF) method, one of the design quantitative procedures for enhancing resistance to progressive collapse. In addition, in order to demonstrate the suitability and applicability of the TF method, the structural robustness and resistance to progressive collapse of the two designs is compared.

Assessment of Seismic Vulnerability of Reinforced Concrete Frame buildings

Assessment of Seismic Vulnerability of Reinforced Concrete Frame buildings