Seismic Provisions Research Articles

Elastic and inelastic acceleration amplification of nonstructural components characterized using recorded building responses

This paper presents a comprehensive study of the acceleration (or force) amplification behavior of building nonstructural components characterized using a large set of recorded building responses available in the Center for Engineering Strong Motion Data (CESMD) repository. The elastic acceleration amplification demands of nonstructural components are analyzed statistically and subsequently compared with the corresponding inelastic demands characterized by the constant-ductility floor response spectra. Different simplified hysteretic rules are adopted for evaluating the inelastic acceleration responses of nonstructural components. The numerical study demonstrates that the elastic acceleration amplification characteristics of the nonstructural components are highly dependent on their natural periods relative to the specific vibration modes of the supporting structures as well as their attachment locations relative to the building height. The presence of component ductility effectively reduces their seismic acceleration demands, particularly in period ranges tuned with their supporting structures. Furthermore, the hysteretic behavior of nonstructural components may moderately modify their acceleration amplification effects. Findings from this study substantiate current seismic design provisions of nonstructural components with evidence derived from building floor responses recorded during real earthquakes.

Column Link Behavior in Eccentrically Braced Composite 3-Dimensional Frames

Eccentrically braced frames are renowned for their capacity to absorb seismic forces while offering greater adaptability. These frames incorporate bracings that are joined to the beams with an intentional offset, forming a connection within the beams. Nevertheless, there are drawbacks associated with implementing these beam connections when renovating frames. This paper seeks to enhance the design approach by introducing an eccentric link within the column of a composite structure. Eccentric braced frames (EBFs) are hybrid systems that offer both ductility in moment resisting frames (MRFs) and lateral stiffening in the concentrically braced system. The study examines composite frames with 5, 10, and 15 stories using eccentric X- and V-type bracings with an eccentricity of 0.5 m and 1 m. Three different earthquake zones are considered, based on Indian seismic code provisions: zone 3, zone 4, and zone 5. The structures are analyzed computationally by nonlinear time history analyses. The lateral load-resisting behavior of the structure with the same eccentricity in beam links and column links is compared. Then, the structure is subjected to a pushover analysis to study the performance characteristics such as capacity curve, lateral displacement, inter-storey drift, and plastification of the structure. As anticipated, compared to conventional moment resisting frames (MRFs) and concentrically braced frames (CBFs), eccentrically braced frames have better energy dissipation. Furthermore, the behavior of X-braced column links is found to be similar to the performance of beam links, but V-braced frames showed better performance in column link frames than in beam link frames. Also, the increase of the link length played a major role in the ductility of the frames.

Stiffening of I-section MRF beams against degradation due to local buckling

Moment resisting frame (MRF) beams under cyclic loading are vulnerable to local flange and web buckling. The Seismic Provisions for Structural Steel Buildings (AISC341) prescribe width-to-thickness ratio limits, which are contingent on target rotations during predefined cyclic loadings. Some rolled I-sections available in the market cannot be employed in special MRFs since they fall short of satisfying the AISC341 flange slenderness limit. Moreover, local buckling leads to a decrease in both strength and stiffness in cyclically loaded MRF beams, ultimately increasing the risk of frame side-sway collapse. This paper introduces a stiffening method aimed at improving the behavior of I-section MRF beams. The proposed method involves placing a pair of stiffeners at the plastic hinge regions. A two-phase numerical study was conducted to assess the effectiveness of this approach. In the first phase, nine unstiffened beam cross-sections with varying flange and web slenderness were considered. The slenderness limits specified by AISC341 were evaluated based on cyclic analyses of these beams. In the second phase, a parametric study was conducted on the same cross-sections, with the flange width and the placement of the pair of stiffeners considered as variables. The results revealed a substantial improvement in behavior with the addition of a pair of stiffeners. Cross-sections that failed to meet the flange slenderness limit could be used in MRFs when stiffened. The optimal location for the stiffeners was found to be significantly influenced by the flange width. Design recommendations for the ideal stiffener placement are presented in this paper.

Equipment response spectra for wind turbines considering the baseline control system

As more and more wind turbines are installed in areas with high seismic intensity, various published works have studied the seismic performance of wind turbines. However, these studies usually focus on the wind turbine, and less attention is paid to the electrical equipment mounted on the wind turbine. Electrical equipment is a non-structural component on wind turbine, which is prone to failure and damage, resulting in the loss of function of the wind turbine. Therefore, it is necessary to study the seismic performance of the electrical equipment installed on the wind turbine. This study focuses on evaluating and quantifying the dependence of equipment spectrum accelerations on the location of the electrical equipment in the structure, the damping ratio of the equipment, and the baseline control system. The baseline control system is used to control the output power by adjusting the rotor speed and the blade pitch angle, which affects the equipment spectrum of the wind turbines. There is a stronger relationship between the equipment response spectrum and the peak floor acceleration. Therefore, the equipment spectral amplification function is calculated as the ratio of the equipment spectral acceleration to the peak floor acceleration for different height. The equipment spectra amplification function is proposed and validated to estimate peak acceleration demands on the design of electrical equipment placed on wind turbines. The results indicate that current seismic code provisions will not always provide an adequate characterization of equipment accelerations. And the effect of wind turbine baseline control and equipment damping is more pronounced in the range of the structural tuning period than in the non-tuning range.

Improved computational methods for probabilistic liquefaction hazard analysis

Current procedures for analysis of and design against liquefaction hazards focus primarily on the use of probabilistic ground motions at a single ground-shaking hazard level, with the cyclic loading represented by a peak ground acceleration (PGA) corresponding to a target return period and a single representative moment magnitude Mw. These parameters are typically used in conjunction with deterministic simplified procedures for estimating liquefaction triggering and consequences that largely neglect the considerable uncertainties inherent to liquefaction problems. Motivated by these limitations and the resulting inconsistencies in liquefaction design levels, early methods for probabilistic liquefaction hazard analysis (PLHA) were proposed that incorporate the full ground motion hazard space, integrated with probabilistic liquefaction triggering models. Such methods provide liquefaction factor of safety (FSL) hazard curves for standard penetration test (SPT) data. Recognizing the increased use of higher-resolution cone penetrometer test (CPT) data in engineering analysis and design and the potential computational challenges it presents, an expanded suite of probabilistic triggering models, and wider availability of more detailed seismic hazard data, an improved PLHA computational methodology is presented in this study. The methods described utilize the U.S. Geological Survey National Seismic Hazard Model directly through web services to obtain PGA hazard and disaggregation calculations for any site and average shear wave velocity in the upper 30 m of the site (Vs30) in the conterminous United States, to reconstruct the PGA hazard space for use in PLHA calculations, and to employ array calculations for efficient liquefaction hazard curve estimates for the thousands of CPT measurements in a given profile. The framework presented here is modular in nature, and discussion on the use of alternative models and extension to probabilistic liquefaction consequence evaluation is presented. The importance of appropriate representation of probabilistic liquefaction model uncertainties is also highlighted, along with the impacts of different levels of uncertainty on the PLHA calculation. Finally, a potential roadmap for incorporation of the PLHA framework in seismic provisions is presented, with an illustration of how it can address current limitations and impacts in liquefaction hazard analysis and design.

NUMERICAL MODELLING OF REINFORCED CONCRETE FRAMES RETROFITTED WITH BUCKLING RESTRAINED BRACE INCORPORATING STEEL AND SUPERELASTIC SHAPE-MEMORY ALLOY CORES

The numerical response of one-storey reinforced concrete frames designed following design standards before the enactment of modern seismic provisions was investigated in this study using the nonlinear finite element method. An unbraced frame and two frames retrofitted with a buckling restrained brace (BRB) incorporating either a stainless steel or chrome molybdenum core bar were modelled. The nonlinear static reverse cyclic loading performance of the frames was assessed. Modifications to the BRB are proposed to mitigate deficiencies identified with the original BRB and steel core bars. The modified BRB incorporating a superelastic shape-memory alloy (SE-SMA) core bar was further modelled. The results illustrate the benefits of implementing SE-SMA as a retrofit strategy to control permanent displacements. The modified BRB with a SE-SMA core exhibited improved lateral strength and displacement capacities relative to the frames retrofitted with steel cores and the control bare frame.

Finite element analysis of RC moment-resisting frames to assess effective slab width; a parametric study

In reinforced concrete (RC) moment-resisting frames (MRFs) with cast-in-situ slabs, the slab action as tension flange during lateral loading enhances the flexural capacity of beams in negative moments. This enhancement may lead to strong beam-weak column unfavorable failure mode in these structures. Field observations of RC MRFs during strong ground motion indicated that the effective slab width values considered by the seismic provisions of the design codes are not adequate to guarantee the achievement of the design method of weak beam-strong column. An accurate estimation of effective slab width needs to assess factors such as geometrical characteristics of connection, continuity of models, and imposed story drift level. A 3D spatial two-story RC MRF was developed using finite element analysis (FEA) to explore the effect of mentioned factors on effective slab width. For finite element (FE) modeling of RC MRF, the concrete damaged plasticity (CDP) model is applied. The CDP model parameters are defined using a mesh-independent methodology introduced in the literature. Comparing the FEA results and results obtained from three half-scale RC MRFs, tested under reversed cyclic loading conditions showed an excellent correlation. The results predicted by the FE model in terms of lateral load–displacement response, reinforcement yielding sequence, crack patterns, and failure modes had a considerable agreement with test observations. The validated FE model was used to develop the other models to conduct a parametric study in the next step. Geometric parameters studied in this paper through numerical modeling were longitudinal and transverse beam length and height, and cross-sectional column dimension. Results of the parametric study showed that the effect of the ratio of transverse beam length to height is significantly more than the ratio of longitudinal beam length to height. The trend of effective slab width versus story drift depends on connection geometry, especially the ratio of transverse beam length to transverse beam height. Finally, an equation was driven to predict the effective slab width using linear regression analysis.

Seismic Performance of Multistory Chevron‐braced Steel Structures with Yielding Beams

AbstractLateral loads are resisted by braces in concentrically braced frames. Therefore, braces meet the demand for the load combination based on the seismic provisions. The rest of the system including the connections are determined according to the capacity‐based design, where the brace members yield under tension and buckle under compression. Chevron or inverted V‐braced frames are generally preferred because they allow large openings for doors and windows. However, the seismic‐design requirements in current building codes lead to deep, heavy chevron beams to resist the unbalanced load at beam members due to pre‐ and post‐buckling compressive strength deterioration and full tensile yielding of the braces. This results in uneconomical design. Recent large‐scale experiments of chevron‐braced frames have demonstrated that limited beam yielding is not detrimental to chevron‐braced frame behavior and on the contrary, it utilizes a second yielding mechanism and thereby increases the story drift capacity at which the braces fracture. Also, they propose a new design method for chevron braced frame with yielded beam. This paper expands the previous findings by investigating the seismic performance of 9‐story structures which are designed according to provisions and proposed method. Structural analysis program SAP2000 is utilized for linear design by modelling the full‐scale 9‐story building. Nonlinear finite element analysis software Perform 3D is utilized for the nonlinear time history analysis in which only a single chevron braced frame is modelled. Results show that the proposed building design has larger interstory drift ratios. However, the adjusted collapse margin ratio and the collapse probability for maximum considered earthquake satisfy the required limitations. In other words, the proposed chevron frame design offers a more economical alternative with no significant tradeoff in seismic performance.

Frictional mid‐spliced shear links for eccentrically braced frames

AbstractAccording to the AISC Seismic Provisions for Structural Steel Buildings (AISC341‐16) and EC8, the inelastic rotation demand at the design story drift is limited to 0.08 rad for I‐shape shear links in eccentrically braced frames (EBFs). Numerical studies on EBF archetypes show that the single‐sided inelastic rotation demands can be much higher than the limiting value. In addition, these links can fail due to low‐cycle fatigue (LCF) which depends on the loading history. A mid‐spliced end‐plated detachable replaceable link has recently been developed to promote easy replacement of end‐plated links. In this paper, a frictional mid‐spliced shear link is developed to increase the inelastic link rotation capacity and LCF life of shear links. The proposed link utilizes a splice connection at the mid‐length, where frictional faying surfaces are introduced to dissipate energy. Slip at the mid‐splice connection causes a relative vertical displacement between the link ends which eventually reduces the rotation demands on the I‐shape members. Experimental and numerical studies were conducted to study the proposed link concept. Three conventional and eight frictional mid‐spliced links were tested using a nearly full‐scale test setup. The results showed that the proposed links have a pinched link shear versus link rotation response. The links were able to sustain a link rotation demand of 0.23 rad together with a significant increase in their LCF life. Numerical studies were conducted to investigate the link rotation, interstory drift, and residual interstory drift of EBF archetypes equipped with the proposed frictional link.

Cost Estimation of Structural Work for Residential Building with Seismic Design Consideration

The Sumatra-Andaman earthquakes had triggered local earthquakes in Malaysia by reactivation of ancient inactive faults. Previously on 5thJune 2015, Ranau, a region located in Sabah, Malaysia, had experienced a moderate earthquake of Mw6.1. The structural failures occurred because all existing buildings only designed for gravity load without any seismic provision. Recent research work exhibits the seismic designs’ impact on the cost of material and its parameters thatimpact the cost. There are two types reinforced concrete residential buildings called Type 1 and Type 2 for two storey and four storeywhich had been used as models. This research applied four seismicity levels to the reference peak ground acceleration value, αgR= 0.07g, 0.10g, 0.13g & 0.16g, and two soil types: Soil Types B and D. The result shows that for twostorey reinforced concreteresidential buildings on soil types B and D, seismic design increases structural work costs, which is around 0.62% to 1.31% and 0.61% to 2.16%, respectively,for Type 1 modelcompared to non-seismic design. Besides,model Type 2, the increment is around 0.24% to 1.22% and 0.20% to 1.71%, respectively.Otherwise, for reinforced concreteresidential building with four storeyon soil types B and D,the result shows that seismic design tends to have a higher structural work’s costaround 0.41% to 2.48% and 0.98% to 11.23%, respectively, for Type 1 model. Besides, for model Type 2 the increment is around 1.80% to 2.05% and 2.34% to 8.53%, respectively, compared to non-seismicdesign.

Seismic Behavior of Reinforced Concrete Bridge and Control Measures for Seismic Pounding

India has had a variety of the world’s greatest earthquakes within the last century. In fact, quite one half area within the country is taken into account vulnerable to damaging earthquakes. The seismic building design code in India (IS 1893, Part-I) is additionally revised in 2002. The magnitudes of the look seismic forces are considerably enhanced generally, and also the seismic zonation of some regions has also been upgraded. There are many literature (e.g., IITM-SERC Manual, 2005) available that presents step-by- step procedures to gauge multi-storeyed buildings. The attention for existing bridges is relatively less. However, bridges are important components of transportation network in any country. The bridge design codes, in India, don’t have any seismic design provision at this time. A outsized number of bridges are designed and constructed without considering seismic forces. Therefore, it is important to gauge the capacity of existing bridges against seismic force demand. There are presently no comprehensive guidelines to help the practicing structural engineer to gauge existing bridges and suggest design and retrofit schemes. So as handle this this problem, this work aims to hold out a seismic evaluation case study for an existing RC bridge using nonlinear static (pushover) analysis. Nonlinear static (pushover) analysis as per FEMA 356 isn’t compatible for bridge structures. So, within the present study an improved pushover analysis is additionally won’t to verify the results.

Seismic performance of bolted T-stub Beam-to-Box column connection

Using internal continuity plates in box columns due to accessibility problems and complicated detailing of connection was perceived as fraught with shortcomings and limitations. To overcome this deficiency, the effectiveness of external continuity plates in conjugation with T-stub connectors in I-beam to box-column connections under cyclic action is investigated in this study. Three damage control strategies based on the fuse action of T-stubs (T-F), strengthening the connections (T-S), and using reduced beam section (RBS) connections (T-R) are pursued and are compared to a corresponding end-plate connection (E). Nonlinear finite element analyses are conducted using the ABAQUS/STANDARD software on the connections under the qualification cyclic loading conditions to elucidate all the main seismic behavioral aspects, including the strength, initial stiffness, energy dissipation, ductility, von-Mises stress, and equivalent plastic strain distributions of models. First, the accuracy of numerical models is validated by a series of available experimental results. Then, a parametric study is performed on the effects of the moment ratio of the beam to column, the number of continuity plates, stiffeners embedded on the beam, and using high strength materials on the seismic performance of the connections. From the results, it is found that the T-S model was the most efficient among the different connections studied, supplying the stiffness, strength, energy absorption, and ductility increases by 2%, 21%, −17%, and 22%, respectively with respect to the E model, satisfying the requirements of AISC Seismic Provisions for SMF. Increasing the beam-to-column moment ratio and the number of continuity plates, had limited effects by less than 10% on the seismic performance of the connections. In the absence of continuity plates, the connections exhibited worse inelastic seismic performance with decreases in stiffness, strength, and energy dissipation up to 67%, 44%, and 74%, respectively. The T-F connection gained a 13% strength increase and satisfied the AISC requirements when high-strength T-stubs are used. Based on the numerical observations, design strength and rotational stiffness of the proposed connections on the component-based joint design strategies, are finally outlined.

IDA-Based Collapse Safety Assessment of Torsional-Irregular Buildings, Considering Ductility and Damage

The complexity in nonlinear behavior of torsional-irregular buildings in combination with uncertainty due to the natural randomness of earthquake records has been always a main challenge for buildings’ seismic design. To find a solution to this challenge, three reinforced concrete (RC) building archetypes were designed and next developed into their nonlinear models. Nonlinear static (pushover) analyses were performed to calculate the capacity of the archetype models in all principal and non-principal directions while incremental dynamic analyses (IDAs) were conducted by applying 30 accelerograms from both near-field and far-field earthquakes. The IDA capacity curves, collapse fragility curves and log-normal cumulative distribution functions (CDFs) were established by including both the aleatory randomness and epistemic uncertainty. Despite previous studies wherein fragility curves were given by evaluating structures’ collapse along structural reference axes or simply on [Formula: see text], [Formula: see text]-axes, in this paper, possible building collapse on a critical non-principal direction (where maximum seismic response was observed) was simulated and its probability was accounted for developing IDA curves and log-normal CDFs. Accordingly, this issue was mirrored in computing available/acceptable collapse margin ratios (CMRs). In addition to the well-known outline used for calculating CMRs in the literature (that is based on estimation of collapse capacity in terms of earthquake intensity measure (IM)), the framework proposed here includes a new method for calculating the CMRs in terms of displacement-based drift, ductility, and damage. The superiority of the proposed method over the former is consistent with the buildings’ design procedure that is governed by storey drift control rather than base-shear strength. Refined statistics of CMRs given by taking into account displacement-based responses illustrate the available CMRs exceed the acceptable CMRs, meaning that a satisfactory safety margin against collapse will be anticipated in the targeted building class if a suitable yielding mechanism with sufficient ductility is provided for seismic force-resisting system by applying seismic design provisions of the current codes.

Axial-flexural strength of steel-concrete composite shear walls

A predictive equation is proposed for the axial-flexural strength of rectangular and flanged Composite Plate Shear Walls-Concrete Filled (C-PSW/CF), with and without endplates and boundary elements. The proposed equation is based on plastic stress distribution, adjusted by coefficients to account for influential design parameters. The adjustment coefficients are established by a regression analysis performed on the data developed using an extensive numerical parametric study. The continuum-based finite element model used for the simulations is first validated using the available test data. The effects of various design variables, including the aspect ratio, slenderness ratio, reinforcement ratio, axial load ratio, infill concrete compressive strength, and yielding strength of the steel faceplates on axial-moment are then numerically examined. Four cross-sections, including double skin plate, double skin plate with endplates, double skin plate with boundary elements, and double skin plate with flanges, are considered. The results are used to develop a new predictive equation to obtain the flexural strength of C-PSW/CFs in presence of axial loading. The proposed equation is finally validated using the experimental test data and its accuracy is evaluated by comparing it to available predictive equations and the method proposed by the 2016 AISC Seismic Provisions. The results show that the proposed design equation can well predict the flexural moment capacity of C-PSW/CFs with various cross-sections in presence of axial loading.

Multiscale finite element analysis of earthquake-induced damage on underground RC culverts: The role of reinforcing bar corrosion

This study conducted finite element (FE) analysis to investigate the effect of corrosion in the sidewall on the damage to underground reinforced concrete (RC) culverts under an earthquake. The rationality of the numerical model was validated through the analysis of quasi-static cyclic loading tests of corroded RC culverts. Based on the validated FE model, a nonlinear dynamic analysis of an underground RC culvert subjected to an earthquake was performed. Further, the global and local responses that were changed not only by the corrosion of the sidewall reinforcement, but also by shear reinforcement in the sidewall and magnitude of the earthquake were discussed comprehensively. The analysis results show that the global deformation of the underground RC culvert increases with a higher degree of corrosion of the sidewall reinforcement and that severe local shear crack damage can be concentrated on the concrete web when corrosion cracks exist. In addition, extremely serious damage was induced in the RC culvert when corrosion occurred in the sidewall without proper seismic provisions. Therefore, steel corrosion in an aging underground RC culvert with insufficient shear reinforcement should be closely monitored to prevent its collapse in the event of earthquakes.

Experimental investigation on steel bracing members with bolted gusset plate connections

In concentrically braced frames, low-cycle fatigue failure may occur in the brace or bolted connection due to accumulated damage from multiple earthquakes. However, the current research on the hysteretic behavior and fatigue life of H-shaped bracing members with bolted gusset plate connections is lacking, and there is a notable omission regarding the impact of bolt slippage and plastic deformation within the connection. The objective of this study is to address the aforementioned limitation through pseudo-static tests of 8 steel bracing members with bolted gusset plate connections under different clearances, connection coefficients (akin to Ry used in brace design under AISC 341-16 Seismic Provisions), and loading patterns. Results showed that not all loading patterns were suitable for such tests due to bolt slippage. The strength capacity, energy dissipation capacity and deformability of specimens with five types of clearances displayed small variation in tests. It has been demonstrated that utilizing a connection coefficient (1.03) lower than the prescribed value (1.3) can still result in a favorable hysteretic performance. The effective length factor of the bracing member under double bolted gusset plate connections is estimated to be 0.79, which can provide valuable information for optimizing the brace design. Additionally, a method for predicting the fatigue life of test specimens is proposed. The fatigue performance and failure mode of the bracing members under bolted connections with clearances of 0t, -2t, -4t and -6t (where t represents the thickness of the gusset plate) are superior to those under welded connections.

Evaluation of rapid visual screening assessment of existing buildings using nonlinear numerical analysis

Different methodologies are available in the literature to perform seismic assessment of existing buildings. Amongst the simplified ones, Rapid Visual Screening (RVS) methodologies have been recently developed and proposed. RVS methods are simplified procedures that can be implemented rather quickly for preliminary assessment of building vulnerability without the need to perform a detailed model and numerical analysis. Their application is particularly useful in regions characterised by high seismicity or where an important share of the buildings was not designed according to seismic provisions. The outcome of RVS methods is a safety index, based on the data from simplified forms that are filled during visual inspection of the buildings. For this reason, the accuracy of the results could be significantly affected by building features that cannot be considered by such forms. To address this issue and to evaluate the effectiveness of RVS methods, this paper focuses on the comparison between the results of a specific RVS method and those from advanced numerical modelling and nonlinear analyses of masonry-infilled reinforced concrete buildings. Several case-study buildings were selected from a database developed in the framework of a recently concluded European project, which focused on the seismic risk assessment of residential buildings in Northern Algeria, a seismic prone region. The buildings are analysed using detailed structural finite element models, through both nonlinear static and dynamic analysis, considering also the influence of mechanical and geometrical properties of the masonry infills. The comparison results show that, despite the significant variability observed in the RVS vulnerability assessment outcomes, there is a fair overall match with the nonlinear analysis results, confirming the utility of RVS methods at an initial assessment stage, as well as the need for further extended validation research efforts.

An Overview of Commonly Used Steel Beam-Column Connection in Indonesia for Low-Rise Building

The Indonesian seismic provision for steel structures was initiated in 2002. The use of steel has also been increasing as a choice of structural material since then. However, there are still many weaknesses in the seismic design of steel structures that have been carried out so far. A lot of beam-column connections in steel buildings in Indonesia use a haunch in a moment-resisting connection system. Haunched systems are not described in AISC 358 as permitted connections for earthquake-resistant buildings. Recently, Europe publishes European Prequalified Steel Joints (EqualJoints). There are four types of connections discussed, and one of them is the haunched type connections. The haunched connection meets the seismic requirements to be suitable for use as an earthquake-resistant connection in Europe. This can be used as a reference if we are going to design a haunched connection in Indonesia. However, special attention should be paid to the details. The bolt configuration, the thickness of the end plates, and the shape of the haunch are not like those commonly used in Indonesia, there must be improvements to be adjusted in EqualJoints. So that the performance of the connection against earthquakes becomes more guaranteed.

Cyclic behavior of 3D moment connections subjected to bidirectional load: Experimental approach

This paper presents an experimental research to assess the cyclic behavior of a bolted moment connection with the use of optimized end-plate connected to built-up box column subassemblies subjected to bidirectional and unidirectional loading. Seven real scale specimens were tested: three specimens with four beams connected to column as interior joint, two specimens with two beams connected as corner joint configuration and two specimens with two beams connected to column as interior joint, according the protocol established in AISC Seismic provisions. The seismic performance was evaluated in terms of hysteretic behavior, failure mechanism, stiffness and dissipated energy. The joints studied were manufactured from of hot-rolled I-beams and square built-up box columns. The elements of connection such as bolts, welding, outer stiffeners and end-plates were designed to remain in elastic range from the flexural expected capacity of beams. The results showed that the required minimum moment of 0.8Mp at 0.04 rad of drift angle was achieved for all specimens tested. However, a higher stiffness and resistance was reached in configuration with unidirectional load (interior joint) in comparison to joint subjected to bidirectional load (corner joint). The damage was concentrated uniquely in beams, while an elastic behavior in columns and connection components was reached for 0.04 rad of drift angle. Finally, this moment connection configuration can be used as an alternative to design buildings with special moment frames under bidirectional loading considering the cyclic behavior of joints evaluated.

Evaluation of ground motion parameters and seismic response of reinforced concrete buildings from the Mw 6.9, 2011 Sikkim earthquake

The continuous collision of the Eurasian plate and the Indian plate has resulted in several earthquakes in the Himalayan region. The 6.9 Mw 2011 Sikkim earthquake, which caused immense damage to the built environment in Sikkim, was triggered by an intraplate source on the overriding Eurasian plate. Strong ground motions from the earthquake were recorded at stations established by IIT Roorkee as part of the PESMOS program. In this paper, near-field and far-field ground motions from this earthquake were analyzed to evaluate their key characteristics and examine their time-frequency features by employing Fast Fourier Transforms (FFTs) and Continuous Wavelet Transforms (CWTs). A comparison between the ground motion parameters of near-field and far-field seismic waves highlights the distinct characteristics of near-field ground motions. Additionally, the impact of near-field and far-field ground motions on the seismic response of a code-compliant RC building is investigated. The results from the non-linear time history analyses indicate that the roof displacements, drift ratio and strain induced in the frame elements are less than the code-prescribed maximum limits. Further, the demand and capacity levels for the RC frame elements were evaluated to compute the performance ratios. The results indicate that the extensive damage to reinforced concrete buildings in the 2011 Sikkim quake was primarily due to the non-engineered nature of the structures and also due to the non-compliance of the built structures to the seismic design code provisions.