Life Safety Performance Level Research Articles

Seismic Evaluation of Buildings using Adaptive Force-Based Multimode Pushover Analysis

The conventional pushover method has 2 major drawbacks, it cannot account for the higher mode effect and do not consider the change in lateral load pattern when the structure reaches its inelastic phase. To overcome those limitations, in this research will present the Adaptive Force-Based Multimode Pushover Analysis (AFMP) method, in this method the higher mode effect, and the change in lateral load pattern have already been considered. This research will compare the result of evaluation using triangular and uniform load pattern with the AFMP load pattern using 1, 2, and 3 modal pairs towards its effects on non linier seismic behaviour of a building with the first mode being not dominant. The analysis resulted that using the AFMP method yields to a higher seismic response on the upper floors, caused by the higher being considered in the analysis. The triangular load pattern, resulted in smaller seismic response on all stories than the AFMP method, while the uniform load pattern tends to overestimate the response on the lower floors. Based on the performance criteria of FEMA 356, the conventional pushover resulted in Life safety performance level, while the AFMP also resulted in Life safety performance level.

The quest for resilience: The Chilean practice of seismic design for reinforced concrete buildings

The satisfactory structural behavior observed during large earthquakes and the high seismicity of the country has conditioned the Chilean society to expect immediate occupancy performance level for their buildings under these extreme events, although the seismic design code in Chile mandates only a scope of life safety performance level. Based on observational and statistical evidence from recent strong earthquakes in Chile, it is concluded that the observed seismic resilience of buildings is a consequence of limiting damage, considering that operational performance and life safety are different challenges that require different approaches; furthermore, to provide society with resilient and safe buildings, both challenges must be met simultaneously and not alternatively. The present article describes the concepts, strategies, and future challenges in the context of the Chilean practice, and the authors describe several lessons learned from the design of thousands of concrete buildings that have experienced earthquakes with a magnitude of 8.0 and higher with limited damage; these lessons have proven to be effective in ensuring resilient structural performance under extreme seismic events.

Experimental and numerical study on the structural performance of auxetic-shaped, ring-shaped and unstiffened steel plate shear walls

Structural engineers have always tried to enhance the seismic performance of existing building systems by introducing new solutions to increase the amount of ductility along with dissipated seismic energy. In this regard, this paper presents a new system to improve the structural behavior of unstiffened steel plate shear walls and eliminate the known defects of these efficient seismic-resistant systems. One of the significant drawbacks of unstiffened steel plate shear walls is the pinching of their hysteretic curve that happens due to the early out-of-plane buckling of the infill plate under small shear forces. Therefore, the primary purpose of this study is to reduce the amount of out-of-plane buckling using perforated plates with periodic auxetic-shaped cellular forms, which have a negative Poisson's ratio. To this aim, a parametric study is conducted on 255 finite element models of auxetic-shaped steel plate shear walls using ABAQUS software to select the most efficient configuration considering some design parameters such as the amount of out-of-plane buckling, energy dissipation and strength. Then, two full-scale specimens of the selected models are investigated experimentally under a quasi-static cyclic loading history. Finally, regarding this fact that for broader adoption of a new system, besides its structural performance, the total weight of that structural system is a determinant factor, two 5- and 10-story plane building models with unstiffened and auxetic-shaped steel plate shear walls are designed to have the life safety performance level at the BSE-1 hazard level and they are evaluated by performing nonlinear static analyses. The results show that auxetic-shaped steel plate shear walls, while improving the seismic performance of a building, reduce its weight.

Experimental Investigation on Cyclic Behavior of Reinforced Concrete Coupling Beams Under Quasi-static Loading

The current status of the reinforcement layouts stated in the codes and frequently used in new construction areas needs to be evaluated and determining its effects on the behavior of structural elements may provide essential contributions to the field. For this purpose, conventionally reinforced, diagonally reinforced (confinement of individual diagonals),and diagonally reinforced with full confined section concrete coupling beam specimens were designed according to ACI 318-14 and Turkish Earthquake Code 2018 in this study. ½-scale test specimens with aspect ratio two were tested under quasi-static cyclic loading using a new complex experimental setup. According to the results obtained, while for conventionally reinforced coupling beams ductile hysteretic behavior remained at 2.0% drift, for diagonal reinforced coupling beams it sustained up to 4.0% drift. Although the diagonal reinforcement enhanced ductility capacity of coupling beams compared to conventionally reinforced coupling beams having a comparably low post-elastic behavior, high ductility demands in the code requirements did not meet. For the same reinforcement ratio and layout, individual confinement around diagonal bars retarded bar buckling and ultimate strength and ductility capacity increased slightly compared to diagonally reinforced coupling beam with full confined section. After all, bar buckling that occurred after the life safety performance level given in the codes was seen at 3.5–4.0% drift. Diagonal reinforcing bars ensured life safety performance level up to 4.0% drift, but it remained at 3.0% drift for conventional reinforcement.

Shaking table study on the seismic performance of an Iranian traditional Un-Reinforced Masonry (URM) building

Shaking table experiment for considering the seismic performance of an existing un-reinforced masonry (URM) building with Jack-arch flooring system was performed. This structural system is one of the most common traditional structures, especially in existing traditional school buildings in Iran. The study involved seismic and dynamic identification tests on one model before and after being modified, including URM brick building with two different floor behavior. In the first model, steel tie beams and steel rods were used, according to the recommendation of Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard-2800), to improve the integrity between steel joists and have a stiff diaphragm with continuous loading path. The second model contained a flexible diaphragm. Dynamic identification tests were performed on each model before and after the experiments in order to identify and track changes in their natural period as the experiments progress. Results showed that the integrity of flooring diaphragm had a considerable impact on improving the seismic performance and reducing the seismic vulnerability of URM buildings with respect to control the damage level and limiting the crack occurred in the model. According to the test results, model with integrated stiff in-plane behavior could meet the Life Safety (LS) performance level. The strengthening methodology on the roof distributed the internal forces more appropriately between different elements and took advantage of the strength of different structural elements.

Reliability analysis and multi-level response modification factors for buckling restrained braced frames

This study aims to assess the seismic performance of buckling restrained braced frames (BRBFs) using a probabilistic approach and develop multi-level response modification factors for performance-based design of these systems. Unlike traditional seismic design methods, the proposed response modification factors can take into account the seismic conditions of the site as well as the target design performance level. An engineering damage parameter method (EDP-Based) is adopted for reliability analysis of 4, 8 and 12 storey BRBFs using systems of parallel and serial components. In general, the results demonstrate the high seismic reliability of BRBFs for high levels of earthquake intensity. Considering the axial strain of the brace core as the local damage index, it is shown that the studied models remain in performance levels higher than life safety under the design hazard level (return period of 475 years). The upper bond response modification factor for the life safety and collapse prevention performance levels is estimated to be around 8.4 and 10.0 with the corresponding intensities of 0.68 and 0.85, respectively. Based on the outcomes of this study, in general, using a response modification factor between 4 and 8 for seismic design of BRBFs would guaranty their adequate performance under both the design basis and maximum considered earthquake levels.

BEHAVIOR OF INDUSTRIAL BUILDING UNDER SEISMIC LOADING

Every year, earthquakes cause injuries, deaths, severe structural damage to buildings anddestruction of property in many countries. In developing countries, economic growth depends on industrialdevelopment. Therefore, if an earthquake occurs, it may cause severe damage to large industrial factories. Thispresent study aims to examine the structural behavior of industrial buildings under the earthquake force whichis a reinforced concrete building. The structure of an industrial building is different from a general building. Inthis study, the factory is a four-story building with the dimensions of 34.4 meters in width, 59.2 meters inlength and 16.2 meters in height. In the analysis, the nonlinear dynamic procedure is applied to analyze thebuilding behaviors. The 20 seismic waves are selected and adjusted with the ASCE41-13. LMSR wave areconsidered in x-direction and y-direction. From the results, the responses and damage of the industrial structureare analyzed. The building has performed the soft story irregularity. The performance level for the acceptancecriteria, according to ASCE41-13 and FEMA365 is life safety performance level. Therefore, the industrialfactory building is needed to enhance the seismic capacity for damage prevention.

Performance-based seismic assessment of precast ferrocement walls for one and two-storey housing

In recent years, innovative structural systems based on Precast Ferrocement Walls (PFW) have been proposed for one and two-storey housing so as to lessen the housing deficiency. This article presents the results drawn from cycling loading tests carried out over two types of PFWs, in order to determine their strength, hysteretic behavior, ductility, energy dissipation capacity, equivalent viscous damping, and damage limit states. These walls have similar structural systems that differ only in the type of reinforcement. To assess their seismic performances for two earthquake hazard levels, a nonlinear dynamic analysis methodology based on the Performance-Based Seismic Design philosophy was developed, which uses the Mostaghel’s multilinear hysteretic model to simulate accurately the actual inelastic behavior and energy dissipation capacity of the PFWs, together with the incremental dynamic analysis (IDA) technique. The Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) structural performance levels were considered and related to the damage limit states. Finally, the performance points of both PFWs fell within the IO range with a 100% probability of incurring no structural damage state for both earthquake hazard levels, which demonstrates their good seismic performance.

Seismic performance assessment of two‐storey precast reinforced concrete building

AbstractIn precast construction, standardized concrete elements are manufactured in a controlled environment followed by onsite installations. One such precast system is 3S building system (Strength, Safety, and Speed), which consists of RCC hollow columns with notches; RCC solid beams (“T” shape/“L” shape/Square Shape), RCC Stair flights, RCC shear walls, and Autoclave Aerated Concrete (AAC) or RCC precast slab. The current study focuses on seismic performance of this system, where a full‐scale two storey, “3S” precast RC building, was subjected to quasi‐static lateral loading. The experimental results show that the structure responded within elastic range at Life Safety (LS) performance level with minimal damage to the joints. The results are further compared to an analytical model in SAP2000 subjected to pushover analysis. Both the experimental and analytical results were found to be in agreement. Therefore, it is inferred that the 3S building system can perform satisfactorily under seismic loads.

Improved seismic design method for steel moment frames

Force-based and displacement-based methods are two conventional approaches for the seismic design of structures. Recently, the advantages and disadvantages of these methods have activated the researchers to combine them and to introduce the hybrid force–displacement (HFD) seismic design methods. In this paper, a new method named “modified seismic coefficient” for steel moment frames (MRFs) is presented. For this purpose, the seismic behavior factor and response spectrum of the structure are determined based on actual structural response and also the fundamental period of the structure. For practical examples, at first, a series of three (3, 6, and 9-story) MRFs is designed based on the proposed method and a classic HFD method, and then, their seismic responses are evaluated using nonlinear time-history analyses. For satisfying life safety (LS) performance level, it is observed that the proposed method reduces structural weight as 27, 22, and 24% for 3, 6, and 9-story frames, respectively.

Application of Direct Displacement Based Design of Reinforced Concrete Frames Subjected To Earthquake Loads

Numerous studies are reported in literature on performance evaluation and rehabilitation of building however, limited studies are reported on performance based design of new buildings. Displacement based design procedure is a new method which is not available in Indian building design codes. An effort has been done to investigate the Direct Displacement Based Design (DDBD) for four, eight and twelve story regular RC frame buildings proposed by Priestley et al, using Indian code Response Spectrum for Zone V which is considered as a very high intensity seismic risk zone for life safety and collapse prevention performance levels. Nonlinear time history analysis is carried out for available ground motion and compared with the performance levels (in terms of drift, displacement). Observations show that design displacement reduction factor should be different for life safety and collapse prevention levels. The effective damping increases as the height of the building increases and is higher for collapse prevention.

Using concentric and zipper steel braces by comparison of effect on improved seismic performance level of concrete moment frame structures with moderate ductility

Recent earthquakes have revealed that, in many cases, the design codes may not guarantee the integrity of all structures for the life safety performance level. Therefore, it seems necessary to study the performance of designed buildings in order to complete, develop and amend the codes. In this paper, the performance level was investigated using the nonlinear static analysis in concrete buildings with moderate ductility and designed according to the latest regulations. Then, as the life safety performance level was not achieved and due to the ease of implementation of steel braces, the concentric chevron brace was used to improve the performance level of these buildings in large bays, and the zipper steel brace was used. The results show that the zipper brace used for strengthening the reinforced concrete structures will increase the performance as well as the stiffness, without the need to strengthen the beams and columns.

Optimal FRP Jacket Placement in RC Frame Structures Towards a Resilient Seismic Design

This paper proposes an optimal plan for seismically retrofitting reinforced concrete (RC) frame structures. In this method, the columns are wrapped by fiber-reinforced polymer (FRP) layers along their plastic hinges. This technique enhances their ductility and increases the resiliency of the structure. Two meta-heuristic algorithms (i.e., genetic algorithm and particle swarm optimization) are adopted for this purpose. The number of FRP layers is assumed to be the design variable. The objective of the optimization procedure was to provide a uniform usage of plastic hinge rotation capacity for all the columns, while minimizing the consumption of the FRP materials. Toward this aim, a single objective function containing penalty terms is introduced. The seismic performance of the case study RC frame was assessed by means of nonlinear pushover analyses, and the capacity of the plastic hinge rotation for FRP-confined columns was evaluated at the life safety performance level. The proposed framework was then applied to a non-ductile low-rise RC frame structure. The optimal retrofit scheme for the frame was determined, and the capacity curve, inter-story drift ratios, and fragility functions were computed and compared with alternative retrofit schemes. The proposed algorithm offers a unique technique for the design of more resilient structures.

An Investigation on the Effect of the Near-Fault Earthquakes on the Seismic Behavior of RC Moment Resisting Frames (MRFs) Designed Based on Iranian Seismic Code (Standard No. 2800)

Past severe earthquakes, such as Bam earthquake of 2003 and Tabas earthquake of 1978, have demonstrated that many cities in Iran are prone to be struck by near-fault earthquakes. Such earthquakes are impulsive in nature, and therefore, they are more destructive than the ordinary ground shaking. In the fourth edition of Iranian seismic code (Standard No. 2800), some changes, including a modification factor for the elastic acceleration response spectrum (EARS) have been recently recommended to reflect the effects of such probable near-fault earthquakes for the designing procedure. In this study, a numbers of 2D RC moment resisting frames (MRFs), from four to twelve story buildings, are designed linearly based on Iranian National Building Code (INBC) and Standard No. 2800 as well. Subsequently, their nonlinear models are reproduced for conducting nonlinear dynamic time history (NDTH) analysis. For this purpose, twenty impulsive ground motions are selected and scaled to be compatible with the design basis earthquake (DBE) spectrum of the abovementioned code. It is concluded that the seismic performance of the analyzed structures are not satisfactory at all; no buildings are successful to satisfy the life safety (LS) performance level posed by guidelines such as ASCE41-06 or ASCE41-13. Moreover, it is worth mentioning that even collapse prevention (CP) limit states are not also met in some cases. Therefore, the recently added modifications in the Standard No. 2800 may be inadequate to incorporate the near-fault earthquakes' effects.

An experimental study on the effect of frame-to-wall connection type on the seismic behavior of steel frames infilled with autoclave-cured aerated concrete blocks

In this article, in order to find some reliable connection types for avoiding the infill failure, an experimental study is conducted on six half-scale single-story single-bay specimens, including one bare frame and five steel frames with autoclave-cured aerated concrete walls, each having different frame-to-wall connection types. Polyurethane adhesive was used in bed joints of the autoclave-cured aerated concrete walls as a mortar. The specimens were tested under displacement-controlled loading to examine their effect on the in-plane behavior of steel frames. The results suggested that V- and T-shaped connectors can be used as prequalified connectors between the wall and the frame. In specimens with these connectors, the interaction between infill and frame was ignorable and the infill remained intact up to life safety performance level (2.5% drift ratio). Furthermore, the application of these connectors resulted in a two-level performance of the infill whereby the frame stiffness degradation and strength deterioration after the drift ratio of 2.5% was compensated.

Probabilistic seismic collapse and residual drift assessment of smart buildings equipped with shape memory alloy connections

This paper probabilistically evaluates the seismic performance of the smart buildings equipped with newly developed shape memory alloy (SMA) connections. The smart structures of this study are those not only can control maximum interstory drifts approximately similar to conventional buildings but also can substantially reduce residual interstory drifts somehow that most of the nonlinear deformations are gathered in SMA fuse bolts. These smart buildings have low cost repair after moderate to severe earthquake events. Although “yielding” of steel structural elements is a design solution employed for dissipation of energy in structures and plastic deformation capacity of members is controlled by design codes for life safety performance level, the damage taken by deformed elements, corresponding residual drifts, and its economic loss after a serious seismic event is undeniable. In order to investigate the combined effects of SMA usage in smart structures including reduction of energy dissipation as a negative impact and removal of residual drift as a positive impact in comparison with conventional structures, superelastic SMA bolts are employed into the connections of two prevalent lateral load-resisting systems, i.e., moment-resisting frame (MRF) and eccentric braced frame (EBF). At first, proper configurations for the beam-column connections of MRFs and the link-beam connections of EBFs are selected from previous research works and validation of the finite element models of them are carried out. Then numerical models of the selected lateral load-resisting systems with and without SMA connections are developed using 4- and 8-story MRFs and EBFs of code-compliant NIST buildings (NIST Technical Note 1863-3). Afterwards, all the buildings are subjected to quasi-static cyclic loading and incremental dynamic analysis (IDA), so the power of employing SMA connections on seismic performance of the buildings would be investigated through seismic concepts. Based on the results, utilizing SMA connections in smart buildings not only could keep interstory drift control performance almost similar to conventional buildings but also could substantially reduce economic loss with significant control of unwanted residual deformations in structural fuses due to their unique ability of induced “recentering” behavior in structural performance. The results probabilistically determine the seismic performance acceptability of studied smart buildings based on the impact of key structural response parameters (i.e., maximum interstory drift, residual interstory drift, and energy dissipation) on the seismic performance of the structure.

Analytical Modeling of Moderately Ductile RC Frame Structures for Seismic Performance Evaluation Using PERFORM-3D

Performance-based vulnerability assessment of buildings requires dynamic inelastic analysis, which cannot be conducted without reliable analytical models. An important aspect of analytical building models involves hysteretic modeling of force-deformation relationships. PERFORM-3D software was used to generate fragility curves for moderately ductile buildings in Eastern Canada using hysteretic models with different features reflecting the recommendations of different North American standards. Two-story and five-story reinforced concrete (RC) frame buildings were considered for this purpose. The parameters that define rotational limits, as specified in ASCE 41-13 and ACI 369R-11 as well as the National Building Code of Canada (NBCC), were assessed. The results indicate that the variations in modeling parameters did not result in significant differences in fragility response at immediate occupancy and life safety performance levels, whereas the fragilities at the collapse performance level were affected. The probability of exceeding collapse prevention in buildings modeled as per NBCC was higher than those modeled using the ASCE 41-13 and ACI 369R-11 requirements.

The effects of viscous dampers on the reliability of steel structures using a PIF index

A new comparative performance measure based on a structure's seismic fragility curve is introduced. This factor, called the performance improvement factor (PIF), was used to compare the seismic performance and reliability of two structures. Using the PIF, the efficiency of viscous dampers on the behaviour of a weak mid-rise steel structure was investigated. A prototype five-span 12-storey steel frame was equipped with three patterns of viscous dampers and their seismic performance was studied. The distribution of dampers along the height of the structure was optimised in three hazard levels using a genetic algorithm and the structure was subjected to 12 ground motion records scaled to levels of 50%, 10% and 2% probability of exceedance in 50 years. The objective function of the optimisation process was defined to achieve immediate occupation, life safety and collapse prevention performance levels at each of the three considered hazard levels. The performance of the primary and rehabilitated structures was investigated using fragility curves and the PIF. A larger PIF indicates a more effective improvement in seismic performance and structural reliability. The results indicate that the suggested method is an effective approach to study and compare the seismic reliability of steel structures.

Investigating the Behavior of Buildings under the Effect of the New Design Ground Motion of Iraq

Recently, Iraq has experienced an increase in seismic activity, especially, near the east boundary with Iran which enhanced the need to study its effect on the behavior of buildings. In this study, a comprehensive methodology was applied to investigate the behavior of a moment frame system with respect to its height after subjected to the design ground motion at Baghdad according to the recently developed seismic hazard maps and, after developing and designing the required configurations of archetype models, specifying life safety as an aimed performance level, modeling nonlinearity and applying the nonlinear static analysis (NSP) according to ASCE/SEI41-13, FEMA356 and FEMA P-695. This methodology is started by sizing members cross-sectional dimensions and applying reinforcement detailing requirements according to ACI318-14. Results show that, for a given building height and number of bays, inelastic drifts increase with decreasing the bay width because the overall building stiffness is decreased and it will be more slender, and consequently, the P- delta effects increased. Also, as the building height increased, both, target and minimum shear capacities decrease and the target displacement increases under the effect of the same earthquake ground motion. Consequently, a necessary limitation on the height of these buildings were deduced to ensure their ability to withstand the future ground shaking and, in the same time, maintaining the life safety performance level of damage. Where, it is found that the maximum allowed heights of framed buildings in Baghdad are 17, 25 and 32 stories for 6, 7.5 and 9 m bay widths, respectively.

Seismic Performance of High-Rise Condominium Building during the 2015 Gorkha Earthquake Sequence

On 25 April 2015, a strong earthquake of magnitude 7.8 struck central Nepal including the capital city, Kathmandu. Several powerful aftershocks of magnitude 6.7, 6.9 and 7.3 together with hundreds of aftershocks of local magnitude greater than 4 hit the same area until May 2015. This earthquake sequence resulted in considerable damage to the reinforced concrete buildings apart from brick and stone masonry constructions. High-rise buildings in Nepal are mainly confined in Kathmandu valley and their performance was found to be in the life safety to collapse prevention level during the Gorkha earthquake sequence. In this paper, seismic performance assessment of a reinforced concrete apartment building with brick infill masonry walls that sustained life safety performance level is presented. Rapid visual assessment performed after the 12 May aftershock (MW 7.3) highlighted the need for detailed assessment, thus, we carried out nonlinear time history analysis using the recorded accelerograms. The building was first simulated for the recorded acceleration time history (PGA = 0.16 g) and the PGA was scaled up to 0.36 g to assess the behaviour of building in the case of the maximum considered earthquake occurrence. The sum of results and observations highlighted that the building sustained minor damage due to low PGA occurrence during the Gorkha earthquake and considerable damage would have occurred in the case of 0.36 g PGA.