Prediction of local seismic damage in steel moment resisting frames

Steel moment resisting frames (SMRFs) are widely utilized as a lateral load resisting system. Their seismic performance is usually assessed by examining the maximum value of inter-storey drift (MID) of all floors. The accuracy of such assessment is debatable given the wide spread of values of MID at collapse that exist in the literature. In this study, a simplified method to define the failure inter-storey drift for each floor of a SMRF is proposed. The method was validated with the experimental and analytical studies by other researchers. Three- and ten-storey SMRFs were considered to further validate the proposed method. The effects of the vertical and/or horizontal seismic components of five different ground motions on the SMRFs were evaluated using incremental dynamic analysis. The proposed method accurately identified the severely damaged floors of SMRFs

Seismic performance of modular steel frames equipped with shape memory alloy braces

The demand for modular steel buildings (MSBs) has increased because of the improved quality, fast on-site installation, and lower cost of construction. Steel braced frames are usually utilized to form the lateral load resisting system of MSBs. During earthquakes, the seismic energy is dissipated through yielding of the components of the braced frames, which results in residual drifts. Excessive residual drifts complicate the repair of damaged structures or render them irreparable. Researchers have investigated the use of superelastic shape memory alloys (SMAs) in steel structures to reduce the seismic residual deformations. This study explores the potential of using SMA braces to improve the seismic performance of typical modular steel braced frames. The study utilizes incremental dynamic analysis to judge on the benefits of using such a system. It is observed that utilizing superelastic SMA braces at strategic locations can significantly reduce the inter-storey residual drifts

Seismic Performance of Modular Steel-Braced Frames Utilizing Superelastic Shape Memory Alloy Bolts in the Vertical Module Connections

In modular construction, individual modules are constructed at a controlled industrial environment before being transported to site. They are then connected horizontally and vertically to form a structure. The vertical connections can be achieved by welding or bolting the columns of stacked modules. This study investigates the seismic performance of modular steel-braced frames (MSBFs) connected vertically using superelastic shape memory alloy (SMA) bolts. The study also identifies the required locations of SMA connections, in a typical MSBF, to optimize its seismic performance in terms of maximum inter-story drift (MID), maximum residual inter-story residual drift (MRID), and damage scheme

STR-834: SEISMIC PERFORMANCE OF MODULAR STEEL FRAMES EQUIPPED WITH SHAPE MEMORY ALLOY BRACES

Modular steel buildings (MSBs) are widely used for one to six storey schools, apartments, and similar buildings, where repetitive units are required. Modular units are first built and finished under a controlled manufacturing environment. They are then transported to the building site, where they are connected horizontally and vertically. The lateral load resisting system for MSBs usually relies on steel braced frames, which dissipate the seismic energy through steel yielding. This behaviour leads to residual drifts complicating the repair of seismically damaged buildings or rendering them as irreparable. Systems that can minimize the seismic residual drifts are thus needed. Superelastic Shape Memory Alloys (SMAs) have the ability to undergo large plastic deformations and recover them upon unloading. Their utilization in steel structures can significantly reduce seismic residual deformations, which will facilitate post-seismic retrofitting. The purpose of this study is to examine the seismic performance of modular steel braced frame (MSBF) that utilizes SMA braces. A six-storey buckling restrained MSBF was considered as a case study. Nonlinear dynamic analysis was conducted to compare the seismic performance of this MSBF when it is fitted with steel and SMA braces. The use of SMA braces was found to improve the seismic performance of MSBs in terms of maximum residual inter storey drift (MRID) and damage scheme

Seismic performance of steel moment resisting frames utilizing superelastic shape memory alloys

Steel structures dissipate the seismic energy through steel yielding, which results in residual deformations. Although conventional earthquake-resisting structural systems provide adequate seismic safety, they experience significant structural damage when exposed to strong ground shaking. Seismic residual drifts complicate the repair of damaged structures or render the structure as irreparable. Therefore, systems that can minimize the seismic residual deformations are needed. Superelastic shape memory alloys (SMAs) have the ability to undergo large deformations and recover all plastic deformations upon unloading. Their utilization in steel structures can significantly reduce seismic residual deformations, which will facilitate post-seismic retrofitting. Although the literature provides few research data on using SMA in steel beam-column connections, previous research did not address their optimum use. This paper identifies the required locations of SMA connections in a typical steel moment resisting frame to enhance its seismic performance in terms of maximum inter-storey drift, residual deformations, and damage scheme

Shape Memory Alloy Reinforced Concrete Frames Vulnerable to Strong Vertical Excitations

Reinforced concrete (RC) framed buildings dissipate the seismic energy through yielding of the reinforcing bars. This yielding jeopardizes the serviceability of these buildings as it results in residual lateral deformations. Superelastic shape memory alloys (SMAs) can recover inelastic strains by stress removal. This paper extends previous research by the authors that optimized the use of SMA bars in RC frames considering the horizontal seismic excitation by addressing the effect of the vertical seismic excitation. A steel RC six-storey building designed according to current seismic standards is considered as case study. Five different earthquake records with strong vertical components are selected for the nonlinear dynamic analysis. The results were used to evaluate the effect of the vertical excitation on the optimum locations of SMA bars

STR-852: PERFORMANCE ASSESSMENT OF THREE-STORY SHAPE MEMORY ALLOY REINFORCED CONCRETE WALLS

The need for sustainable structures, that provide adequate ductility without experiencing major damage, has led researchers to develop methods to achieve self-centering structures. One of these methods involves the use of superelastic Shape Memory Alloy (SMA) bars. This study assesses the seismic performance of a three-story SMA Reinforced Concrete (RC) shear wall considering different potential locations for the SMA bars. The maximum inter-story drift, residual drift, and damage scheme are evaluated using Incremental Dynamic Analysis (IDA). The use of SMA bars at the plastic hinge of the first floor was found to significantly reduce the residual drifts and associated damage

Seismic fragility assessment of superelastic shape memory alloy reinforced concrete shear walls

Mitigation of seismic damage can be achieved through self-centering techniques. One of the potential techniques involves the use of Superelastic Shape Memory Alloy (SE-SMA) bars in Reinforced Concrete (RC) structures. This study explores the use of such bars in the plastic-hinge regions of RC walls. The seismic performance and vulnerability of SE‑SMA RC walls of ten- and twenty-story buildings are analytically assessed using fragility curves. The maximum inter-story drift, residual drift, and fragility are evaluated using multi strip analysis. The results clearly demonstrate the superior seismic performance of SE-SMA RC walls as compared to steel RC walls

Assessment of the flexural behavior of reinforced concrete beams strengthened with concrete jackets

Analysis of continuous jacketed Reinforced Concrete (RC) beams requires accounting for the nonlinear behavior of the interface and the materials as well as redistribution of moments. This kind of analysis is complex and require an advanced level of knowledge and experience to perform. Engineers need simplified yet robust tools to practically predict the actual behavior of jacketed RC beams. In the current practice, slip is neglected in the analysis and monolithic behavior is assumed for the jacketed section, which result in higher estimates of stiffness and/or capacity. This paper provides a simplified method to analyze continuous jacketed RC beams taking into account the interfacial slip distribution and the actual nonlinear behavior of both concrete and steel. An iterative calculation algorithm is developed to determine the moment–curvature curves of a jacketed beam at different sections. The developed method allows the evaluation of interfacial slip and shear stress distributions in ductile reinforced concrete beams. The developed method is utilized to conduct an extensive parametric study, which resulted into modification factors that can be used to calculate the capacity and deformations of a strengthened beam considering the interfacial slip

Equivalent standard fire duration to evaluate internal temperatures in natural fire exposed RC beams

With the recent shift towards performance-based fire design, practical methods to account for natural fire loading when designing concrete structures are needed. Available design methods and analysis approaches are based on standard fire curves. To apply these methods, a natural fire event can be converted to a standard fire with a specific duration (time equivalent). However, existing time equivalents often ignore the influence of internal temperature gradients on the section behaviour, which is unacceptable for concrete structures. This paper introduces a time equivalent method suitable for reinforced concrete (RC) beams exposed to natural fire. The method is based on the actual temperature gradient within a concrete section. To simplify analysis of RC beams exposed to fire, an average internal temperature profile (AITP) can be utilized, which records the average temperature variation along the height of a section. Two equations are provided such that a standard fire duration can be determined to accurately or conservatively represent the AITP of a beam section exposed to natural fire. Characteristics of the natural fire, as well as the influence of section dimensions are accounted for. The developed AITP time equivalent method is found to be superior to the existing methods and accurate in approximating the moment-curvature response for RC beam sections