Low-rise Steel Buildings Research Articles

Structural Evaluation of a Low-Rise Steel Building in Jakarta

Structural Evaluation of a Low-Rise Steel Building in Jakarta

Experimental study of wind-induced dynamic response and collapse of a mechanically-attached membrane roofing system installed on metal substrate of flat-roofed low-rise steel building

This paper investigates the wind-induced dynamic response at design wind speed and the collapse of a mechanically-attached membrane roofing system installed on metal substrate of flat-roofed low-rise steel building, based on a wind pressure loading test using full-scale assembly specimens. Three kinds of waterproofing membranes with different mechanical properties are tested. The wind loads employed in the test are generated by using the time histories of wind pressure coefficients on the roof of a flat-roofed low-rise building with low parapets, which were obtained from a wind tunnel experiment. Both the temporal and spatial variations of wind pressures are reproduced by using three Pressure Loading Actuators (PLAs). A step-wise pressure loading test commonly employed in the conventional wind-resistant performance evaluation in Japan is also carried out for a comparative purpose. The results indicate that the fasteners connecting the disks with the metal substrate are subjected to not only vertical uplift forces due to negative wind pressures (suctions) but also horizontal forces related to the membrane deformation. The maximum value of horizontal force is nearly equal to that of the vertical force. Although the general correlation between vertical and horizontal forces is not so high, the maximum values of these forces may occur almost simultaneously. Larger the membrane deformation, larger the horizontal forces are. The horizontal forces reduce the failure loads and affect the failure modes significantly. Therefore, the effect of horizontal forces should be considered in the evaluation of wind-resistant performance of mechanically-attached membrane roofing systems. The failure load under step-wise pressure is generally smaller than that under fluctuating wind pressures. Therefore, the conventional step-wise pressure loading test can be used as a simple method for evaluating the failure load of the roofing system on the safer side.

Seismic design of low-rise steel building frames with self-centering hybrid damping connections

This paper develops a practice-oriented seismic design procedure for an emerging lateral force resisting system. The system combines the favorable re-centering feature with the attractive hybrid damping capacity. The system overcomes the detrimental frame expansion effect that occurs in conventional self-centering building frames without the cost of building space. Following the proposed design procedure, multiple designs with different parameters to achieve performance objectives were performed for a representative three-story building in which the considered lateral force resisting system is used to resist the seismic forces. Nonlinear response history analyses were performed for the designs to evaluate the applicability and adequacy of the proposed design approach. Based on the analyses conducted in this research, it was found that the considered system designed using the proposed approach can meet both transient and residual inter-story drift requirements specified for the selected performance objectives. While an initial design per the proposed design approach may be inadequate, the re-design strategy recommended can help transform the design to an acceptable one after only one round of modification. Moreover, the composition of hybrid damping may affect the maximum floor acceleration responses. In this study, the maximum floor acceleration can be reduced 12.75% at most by replacing hysteretic damping with viscous damping. This should be included in design consideration in the proposed approach through adjusting the hybrid damping composition.

Assessment of Rotational Stiffness for Metallic Hinged Base Plates under Axial Loads and Moments

Pinned base plate connections are the most common base connection used in low-rise steel buildings. In this research, an extensive parametric study is performed using the Finite Element (FE) software Abaqus to determine the elastic rotational stiffness, moment resistance, and energy absorption of the pinned base plate connection connected to a reinforced concrete footing and subjected to an eccentric axial load. The developed FE model is validated using experimental results from the literature. Moreover, an intensive parametric study is conducted to understand the behavior of these connections better. The investigated parameters include the base plate thickness, anchor bolt diameter, and arrangement and number of bolts. The most effective parameters that affect the elastic rotational stiffness and moment resistance of pinned base connections are the anchor bolt arrangement and diameter. The maximum increase in the rotational stiffness was 53% for the anchor bolt diameter of 30 mm when the base plate thickness increased from 12 mm to 30 mm. Based on the base plate thickness, the moment resistance is improved by 150–260% when the bolt diameter increases from 12 mm to 30 mm.

Experimental study on full-scale steel moment-resisting frames with nonstructural walls subjected to multiple earthquakes

A cyclic loading test of a steel moment-resisting frame (SMRF) with nonstructural components was conducted to evaluate the seismic performance of steel buildings subjected to multiple earthquakes. The specimen is a single-floor, one-span substructure of the intermediate story of typical current middle- or low-rise steel building in Japan. Two specimens were tested. The structural systems of these two specimens were the same, but the nonstructural components attached to the steel frame were different. The light gauge steel (LGS) partition wall and the autoclaved lightweight concrete (ALC) exterior wall were used as the nonstructural components of each specimen. One typical set of loading history that corresponds to one earthquake was created based on the response analysis results, and multiple sets of loadings with various levels were loaded to consider the effect of multiple earthquakes. Based on the observed visible damages, it was found that the structural component performed well under multiple earthquakes with a maximum story drift angle less than 1/50, while for the nonstructural component, the ALC wall performed better than the LGS wall. From the obtained load–deformation relationship, it was found that the strength of the structural component and the strength contribution of the LGS wall gradually decreased when subjected to multiple earthquakes, while the strength contribution of the ALC wall fluctuates within a close range. Moreover, the elastic stiffness of the structural component subjected to multiple earthquakes was almost constant, while the stiffness contribution of the nonstructural components decreased.

Self-centering mechanism and seismic response of steel tension-only concentrically braced beam-through frames

Tension-only concentrically braced beam-through frames (TCBBFs) are a newly proposed structural system that has great potential in damage mitigation for seismic design of low-rise steel buildings. In TCBBFs, columns usually have cold-formed hollow structural section (HSS) and are connected to the flanges of H-shaped beams at each floor level as an easy main frame assembly, and tension-only braces are installed to the main frame to provide additional lateral stiffness. The braces also serve as the replaceable fuse elements that contain the self-centering and energy dissipation properties of the system. This paper investigates the self-centering mechanism, structural behavior, and seismic performance of TCBBFs through integrated analytical and experimental studies. Particularly, shaking table tests were conducted to investigate the seismic response of TCBBFs with tension-only braces designed with four different methods. The effects of yielding, prestress level, and design methods of the braces on structural response are evaluated. The experimental results show that TCBBFs are capable of archiving uniform story drift response with self-centering ability upon unloading. Due to the self-centering mechanism of the system, the tension-only braces can be easily replaced and the main frame can be reused after the shaking of major earthquakes.

Seismic design and performance evaluation of low-rise steel buildings with self-centering energy-absorbing dual rocking core systems under far-field and near-fault ground motions

This research focuses on seismic design and performance evaluation of low-rise steel buildings with self-centering energy-absorbing dual rocking core systems (denoted as SEDRC systems) under far-field and near-fault ground motions. The SEDRC system consists of two rocking cores (RCs) and several shear friction spring dampers (SFSDs). These SFSDs are located between the two RCs and arranged over the height of the SEDRC system to absorb energy and provide a self-centering feature. The two RCs are considered as two buckling restrained braced frames in this paper, which are utilized to obtain uniform inter-story drift distribution in buildings. The two RCs can also act as a backup lateral force-resisting and energy-dissipation system if necessary. A direct displacement-based design (DDBD) procedure is introduced for the SEDRC system. A physical test was conducted to investigate the stability of the SEDRC system under repeated loading with near-fault loading protocol. The test results show that the SEDRC specimen can get stable self-centering behavior under repeated rounds of tests, indicating that the SEDRC system can be fully recoverable against multiple earthquakes before the development of the bearing action in SFSDs. The computational model of the SEDRC system was created and verified with the test results. A three-story representative building was designed through the proposed DDBD method, and the numerical models of the building were generated using the verified modeling method. Forty far-field ground motions and twenty near-fault ground motions were selected to perform Nonlinear Dynamic Analyses (NDA) on the designed building. The NDA results show that the designed three-story SEDRC system can satisfy the drift limit under DBE far-field excitations. And the designed SEDRC system can also survive and achieve small residual drifts subjected to the fault-normal components of the selected near-fault excitations and MCE far-field excitations.

Effect of anchors on the seismic performance of exposed column-base plate weak-axis connections

The number and magnitude of earthcorrquakes are increasing in South Korea. However, unreliable exposed column-base plate connections of low-rise steel buildings are still easily found in the field. Therefore, based on intensive field inspection, six large-scale exposed column-base plate weak-axis connection specimens were examined, under both axial compression and lateral cyclic loading, to develop stable and reliable column-base plate joints in the weak-axis direction. From the test results of the first set of specimens, it was found that the seismic performance of field-representative specimens was quite poor due to a “rocking” phenomenon observed between the base plate and concrete foundation because of the severe residual plastic deformation of round-section anchor bolts. To reduce the rocking phenomenon, a second set of specimens was fabricated and evaluated. By using an eight threaded anchor-layout, the rocking phenomenon was substantially reduced. Therefore, it is strongly recommended to use eight threaded anchors in three rows in order to enhance seismic performance, rather than four in two rows, for exposed column-base plate weak-axis connections.

Seismic design of low-rise steel building frames with self-centering panels and steel strip braces

This paper develops a practical seismic design approach for an emerging lateral force resisting system consisting of self-centering panels and steel strip braces. The system combines the favorable re-centering feature of conventional self-centering building frames and the energy absorption capacity and high initial stiffness of concentrically braced frames. The system also overcomes the detrimental frame expansion effect that occurs in conventional self-centering building frames. Following the proposed design approach, multiple designs to achieve different performance objectives were performed for a representative three-story building in which the considered lateral force resisting system is used to resist the seismic forces. Nonlinear response history analyses were performed for the designs to evaluate the applicability and adequacy of the proposed design approach. Based on the analyses conducted in this research, it was found that the considered system designed using the proposed approach can meet both transient and residual inter-story drift requirements specified for the selected performance objectives. While an initial design per the proposed design approach may be inadequate, the re-design strategy recommended can help transform the design to an acceptable one after only one round of modification. Moreover, the high-mode effect appears nonnegligible in the considered system and this effect should be considered in the proposed approach through the use of the lateral distribution factor of seismic forces specifically for self-centering systems.

Development of improved exposed column-base plate strong-axis joints of low-rise steel buildings

Due to increasing seismic risk, seismic design has become mandatory even for low-rise structures in Republic of Korea since December 2017. However, it is not difficult to find undesirable exposed column-base plate strong-axis joints of low-rise steel buildings in the field. Such undesirable connections might not have sufficient capacity and stability under earthquake. Therefore, a series of experiments were carried out to develop improved exposed column-base plate strong-axis joints of low-rise steel buildings. In total, seven large-scale column-base plate strong-axis connection specimens were investigated under both axial compression and lateral cyclic loading. It was found that the hysteretic behavior of such improper joints typically used in the field was unstable due to a “rocking” phenomenon between a base plate and concrete foundation by large plastic residual deformation of anchor bolts. To overcome the rocking phenomenon, efforts were made to develop enhanced connections. Based on the test results, considerably improved and stable hysteretic behavior without the rocking phenomenon was obtained by using eight threaded anchor bolts. However, further study is needed to assess the effect of eight threaded anchor bolts on the seismic performances of more various connections.

An experimental study on eccentrically braced beam-through steel frames with replaceable shear links

Prefabricated tension-only concentrically braced beam-through frames (BTFs) have received popularity for low-rise steel buildings in low to moderate seismic regions. However, the deteriorating pinched hysteretic behaviour of the tension-only concentric braces limits the energy dissipation capability of such systems under earthquakes. This study presents a modified eccentrically braced lateral force-resisting system aiming to enhance the energy dissipation capability of the BTFs. Meanwhile, seismic resilience is promoted with the utilization of replaceable shear link beams acting as structural fuses. The structural configuration and the basic design concept of the proposed eccentrically braced BTFs is first introduced. The essential mechanical characteristics of this bracing system are subsequently described with a simplified theoretical model. Seven full-scale eccentrically braced BTF specimens are subsequently tested, where the effects of link length, bracing angle, and link section are examined. The test results show that short links tend to improve the stiffness, load resistance and ductility of the BTF due to the exhibited shear-dominant behaviour. An increase in bracing angle leads to increased lateral stiffness and load resistance but at the cost of reduced ductility. Reducing the link section helps delay the development of weld cracks and results in better ductility of the structural fuse. The test results also warn that weld defects and inappropriate design of the link beam would induce brittle weld fractures at the ends of the link and lead to unsatisfactory ductility.

Seismic evaluation of low-rise steel building frames with self-centering energy-absorbing rigid cores designed using a force-based approach

This paper focuses on a new lateral-force-resisting system – the Self-Centering Energy-Absorbing Rigid Core system (denoted as the SCENARIO system)-for achieving enhanced seismic performance and improved post-earthquake reparability in low-rise steel building frames. Friction-Spring Dampers (FSDs) are included in the SCENARIO system to achieve the self-centering feature and dissipate hysteretic energy. Moreover, Buckling Restrained Braces (BRBs) are included in the SCENARIO system to absorb earthquake energy if needed. A design procedure was proposed for the SCENARIO system. Results from Nonlinear Static Analyses (NSA) show that the design procedure can enable the SCENARIO system to exhibit the intended nonlinear behavior. A representative three-story demonstration building was considered in this research to investigate the seismic response of the low-rise steel buildings with the SCENARIO systems to resist the lateral seismic forces. Three designs adopting different response modification factors to determine the design base shears were performed for the demonstration building. Results from Nonlinear Response History Analyses (NRHA) of the considered systems show that the SCENARIO systems can exhibit satisfactory seismic responses when designed with the response modifications factors of 6 and 8 which are assigned to conventional steel braced frames. Moreover, it was found that the residual inter-story drift ratios of the SCENARIO system can be lower than 0.005 rad even under the MCE excitations, creating a satisfactory condition for the post-earthquake repair work if necessary.

Seismic performance improvement of tension-only-braced frames with Energy-Dissipative Rocking Columns

Steel braced frames consisting of strong beams, weak columns, and tension-only braces (BTFs) have been extensively used in low-rise steel buildings, since it is prefabricated rapidly and is cost-efficient. However, BTFs are vulnerable to soft story failure due to the negligible post-yielding stiffness of tension-only braces. A novel device of Energy-Dissipative Rocking Column (EDRC) is proposed to improve the seismic performance of BTFs. An EDRC consists of dual hinge supported steel column branches and replaceable steel strip dampers between them. Firstly, the effectiveness of EDRCs were verified through nonlinear time history analyses on benchmark multi-story BTFs using a suite of far-field ground motion records. Secondly, systematic parametric studies are conducted to quantify the effect of key influencing factors such as stiffness ratio of EDRC to BTF and bending stiffness of column branches on the seismic performance improvement of BTF-EDRC systems. The results show that the maximum inter-story drift and inter-story drift concentration under earthquakes as well as the residual drift after earthquakes can be significantly mitigated by coupling with EDRC. It is found that the maximum inter-story drift ratio can be reduced by 50% when the stiffness ratio of EDRC to BTF reached 1.0. The most effective stiffness ratio of EDRC to BTF for mitigating the inter-story drift concentration and residual drift ratio falls in a range of no more than 0.2 and 0.4, respectively.

Mushroom skeleton to create rocking motion in low-rise steel buildings to improve their seismic performance

Rocking motion have been used for achieving the \'resilient buildings\' against earthquakes in recent studies. Lowrise buildings, unlike the tall ones, because of their small aspect ratio tend to slide rather than move in rocking mode. However, since rocking is more effective in seismic response reduction than sliding, it is desired to create rocking motion in low-rise buildings too. One way for this purpose is making the building\'s structure rock on its internal bay(s) by reducing the number of bays at the lower part of the building\'s skeleton, giving it a mushroom form. In this study \'mushroom skeleton\' has been used for creating multi-story rocking regular steel buildings with square plan to rock on its one-by-one bay central lowest story. To show if this idea is effective, a set of mushroom buildings have been considered, and their seismic responses have been compared with those of their conventional counterparts, designed based on a conventional code. Also, a set of similar buildings with skeleton stronger than code requirement, to have immediate occupancy (IO) performance level, have been considered for comparison. Seismic responses, obtained by nonlinear time history analyses, using scaled three-dimensional accelerograms of selected earthquakes, show that by using appropriate \'mushroom skeleton\' the seismic performance of buildings is upgraded to mostly IO level, while all of the conventional buildings experience collapse prevention (CP) level or beyond. The strong-skeleton buildings mostly present IO performance level as well, however, their base shear and absolute acceleration responses are much higher than the mushroom buildings.

Seismic risk sensitivity of structures equipped with anti-seismic devices with uncertain properties

Damping and isolation devices are often employed to control and enhance the seismic performance of structural systems. However, the effectiveness of these devices in mitigating the seismic risk may be significantly affected by manufacturing tolerances, and systems equipped with devices whose properties deviate from the nominal ones may exhibit a performance very different than expected.The paper analyzes this problem by proposing a general framework for investigating the sensitivity of the seismic risk of structural systems with respect to system properties varying in a prescribed range. The proposed framework is based on the solution of a reliability-based optimization (RBO) problem, aimed to search for the worst combination of the uncertain anti-seismic device parameters, within the allowed range of variation, that maximizes the seismic demand hazard. A hybrid probabilistic approach is employed to speed up the reliability analyses required for evaluating the objective function at each iteration of the RBO process. This approach combines a conditional method for estimating the seismic demand at a given intensity level, with a simulation approach for representing the seismic hazard.The proposed method is applied to evaluate the influence of the variability of the properties of linear and nonlinear fluid viscous dampers on the seismic risk of a low-rise steel building. The study results show that the various response parameters considered are differently affected by the damper properties and unveil the capability of the proposed approach to evaluate the potentially worst conditions that jeopardize the system reliability.

Modeling and seismic collapse resistance study of a steel SC-MRF

A self-centering (SC) moment resisting frame (MRF) is an alternative to a conventional steel special moment resisting frame (SMRF) with welded beam-to-column connections for seismic-resistant steel frame buildings. The beams in an SC-MRF are post-tensioned to the columns by high strength post-tensioning (PT) strands that are oriented parallel to the beams, providing restoring forces to control gap opening at the beam-column interface. Little is known about the collapse resistance of SC-MRFs under extreme seismic ground motions. Incremental Dynamic Analyses (IDA) are performed to determine the collapse margin ratio of a 4-story low-rise steel building with perimeter SC-MRFs. The structural model for the SC-MRF for the IDA includes shell finite elements to enable important limit states, including local buckling in the beams, to be included in the analyses. The results from the IDA show that the collapse resistance of an SC-MRF system is comparable to that of a conventional steel SMRF.

Horizontal seismic force demands on nonstructural components in low-rise steel building frames with tension-only braces

Steel building frames consisting of tension-only braces have been recently recognized as adequate lateral force resisting systems for use in low-rise buildings in the regions with seismicity. To further promote the use of such systems, this investigation was focused on developing recommendations for calculating the horizontal seismic force demands on the nonstructural components attached to the systems. Specifically, two full-scale three-story experimental models were designed, constructed and tested using shake tables. The two experimental models differed from each other primarily in that one model consisted of the exterior walls with non-negligible contributions to the system lateral stiffness while the other experimental model did not have such exterior walls. A series of shake table tests using the excitations scaled to different intensity levels were performed on each experimental model. It was found that the existing design and analysis methods appear inadequate in predicting the horizontal seismic force demands on the nonstructural components. Based on the test results, a practical model which can well capture the central tendency of the test results and can be integrated into the existing design method was developed. Test results also revealed that the exterior walls with non-negligible contributions to the system lateral stiffness can arouse larger horizontal seismic force demands on the nonstructural components.

Using PBEE to assess and improve performance of different structural systems for low-rise steel buildings

Using PBEE to assess and improve performance of different structural systems for low-rise steel buildings

Energy damage index based on capacity and response spectra

Non-linear dynamic analysis and the damage index of Park-Ang have been often used to assess expected seismic damage to a structure. Depending on the size of the structure and the duration of the record, the computational effort in dynamic analyses is usually high. In this research, a new damage index is proposed based on nonlinear static analysis. The damage index is a linear combination of two energy functions: (1) the strain energy associated with the stiffness variation and the ductility of the structure, and (2) the dissipated energy associated with hysteretic cycles. These two energy functions are obtained from the capacity curve of the structure and from the energy balance with the spectral acceleration. To show the ability of the index to represent damage, low-rise steel buildings were studied under the seismic actions that are expected in Mexico City. The results obtained with the new method show good agreement with those calculated by means of dynamic analyses using the Park-Ang damage index. On average, the Park-Ang damage index is well-fitted by the combination of 62% of the strain energy and 38% of the energy dissipated by hysteresis. Moreover, the new damage index can link damage to certain characteristics of seismic actions, such as their intensity and duration. Therefore, the new approach results in a practical, powerful tool for estimating seismic damage in buildings, especially as probabilistic approaches require massive computations.

EFFECTS OF CONNECTION DETAIL ON STRENGTH AND CYCLIC DEFORMATION CAPACITY OF ANGLE BRACE

Braced frame structures are used for low-rise steel buildings with large space such as school gymnasium, and angle braces are often adopted as the main seismic component. These buildings are used as emergency public shelters in event of disaster. Therefore, it is very important to secure the sufficient seismic performance. However, a reconnaissance of the recent earthquake reports that the brittle fracture at the effective cross-section of an angle brace. Single-angle brace has the inevitable eccentricity between the brace and its gusset plate, and this detail is a disadvantage in terms of connection strength. Therefore, in the case of double-angle brace, it is known that the removal of the out-of-plane eccentricity leads to the improvement of the ultimate strength at the effective cross-section. In addition, the previous paper reports that Z-shaped double-angle brace removing both out-of-plane and in-plane eccentricities brings further increase in the ultimate strength at the effective cross-section. On the other hand, the recent studies on double-angle brace point out the decrease in cyclic deformation capacity. A purpose of the present study is to clarify the effect of connection detail on not only strength at the connection but also cyclic deformation capacity of angle brace. In the present paper, both connection tests and component tests were carried out. Specimens of the tests are angle braces connected to gusset plates using high strength bolts. In the connection test, the monotonic tensile loading was employed in order to investigate the effect of connection detail on the ultimate strength. The main parameters were angle cross-section (L65x6, L75x6 or L90x7), thickness of gusset plate (PL9, PL16 or PL19), connection detail (single, double-angle or Z-shaped) and the number of bolts (2 to 5). On the other hand, in the component test, the cyclic loading was employed to verify the influence of connection detail on cyclic deformation capacity of the angle braces. The test parameters were angle cross-section, thickness of gusset plate (PL9, PL12 or PL16), connection detail and loading protocol (incremental or constant amplitude). The result of the connection tests indicates that the effective yielding leg ratio of single-angle brace is independent on the number of bolts, which are approximately constant at about 0.5. However, those of both double-angle and Z-shaped double-angle brace increase in proportion to the number of bolts, whose values are roughly from 0.2 to 1.1. Therefore, it is found that the out-of-plane eccentricity has a great influence on the yield strength at the connection of angle brace. Meanwhile, the ultimate strength at the effective cross-section tends to increase in proportion to the number of bolts. However, the effective leg ratio of the cross-section of both double-angle and Z-shaped double-angle brace is 1.2 times to that of single-angle brace. It means that the removal of out-of-plane and/or in-plane eccentricity has a relatively small effect on the ultimate strength at the effective cross-section. On the other hand, the results of component tests indicate that the cyclic deformation capacity of both double-angle and Z-shaped double-angle brace is much lower than that of the single-angle brace. In the case of L65x6 cross-section, a cumulative plastic ductility ratio of both double-angle and Z-shaped double-angle brace is decrease to roughly 5% to 20% of the single-angle brace. Conclusively, although the removal of the out-of-plane eccentricity brings the increase in the connection strength of angle brace, it causes the decrease of the cyclic deformation capacity as the whole member.