Seismic Provisions Research Articles

Seismic design of steel moment‐resisting knee‐braced frame system by failure mode control

AbstractThis paper presents the seismic design of a steel moment‐resisting knee‐braced frame (MKF) using the theory of plastic mechanism control (TPMC) within the capacity‐based design framework. The MKF is an alternative system to MRFs, wherein knee elements are utilized to provide rigid connections and enhance lateral stiffness. Capacity‐based design, the predominant approach in current seismic provisions, relies on two key principles: (1) selecting specific structural components as fuses with sufficient ductility to dissipate seismic energy, and (2) ensuring non‐fuse elements can resist the maximum probable reactions from these fuses. The ultimate goal is to achieve a global mechanism where yielding occurs in all structural fuses and at the base of first‐story columns. However, existing seismic design provisions often struggle to fully satisfy the second principle due to the lack of a method for controlling failure modes. TPMC addresses this challenge by ensuring compliance with the second principle, grounding its approach in the kinematic method and the mechanism equilibrium curve within the rigid‐plastic analysis framework. By considering all potential story‐based undesirable mechanisms and calculating the required plastic moment of columns up to a target design displacement, TPMC ensures adherence to the second principle of the capacity‐based design approach, leading to the achievement of a global collapse mechanism. In this paper, an iterative method is proposed for designing beams and knee elements by considering plastic hinges at both ends of the beams, followed by a TPMC‐based methodology for designing columns to ensure a global mechanism. A parametric analysis of a single‐story single‐span MKF explores the effects of knee element geometry ( and ) on component demands. The results indicate that optimal parameter ranges of and can minimize the demands for MKF components. Practical design examples are illustrated using three steel MKFs, each consisting of four, seven, and ten stories with five spans. Pushover analysis and nonlinear dynamic analyses were performed to demonstrate the effectiveness of the proposed design procedure in ensuring the attainment of a global mechanism and excellent seismic performance under real ground motions.

Seismic Performance Assessment of Multitiered Steel Buckling-Restrained Braced Frames Designed to 2010 and 2022 AISC Seismic Provisions

Seismic Performance Assessment of Multitiered Steel Buckling-Restrained Braced Frames Designed to 2010 and 2022 AISC Seismic Provisions

Vulnerability of structures designed with seismic provision due to explosions in mines

Vulnerability of structures designed with seismic provision due to explosions in mines

Site-Specific Seismic Hazard Analysis for Shallow Tunnel in Nepal

Abstract Several seismic codes are implemented for the design and construction of superstructures in Nepal but there is no seismic guideline for shallow tunnels which are often constructed using conventional engineering approaches. The uniform hazard spectrum was obtained after performing a Probabilistic Seismic Hazard Analysis at Dhulikhel and the target spectrum was estimated by comparing it with the spectrum recommended by the seismic code of Nepal Building Code NBC 105:2020 and Indian standard IS 1893:2016. The average response spectrum from ten recorded earthquake ground motions was selected from a peer ground motion database with the known shear wave velocity obtained from geophysical survey. The comparative analysis revealed that the design spectra for identical soil classes, as determined by this study are slightly higher than those prescribed by the present seismic code provisions. This finding emphasizes the necessity for developing more specific guidelines tailored to the design of shallow tunnels in Nepal to ensure their structural resilience in the event of an earthquake.

Damage to stone masonry buildings in historical centers due to the 2023 earthquake sequence in Turkey

Unreinforced stone masonry buildings represent a significant part of the building stock in the areas affected by the recent devastating earthquakes of 6 February 2023 in Turkey. Most of them were built before 2000, and, hence, they are not compliant with current seismic provisions. Severe damage or collapse was observed in a large number of low-rise stone masonry buildings, including many listed as monuments ones. The structural systems of masonry buildings in the historical center of two cities (namely, Gaziantep and Antakya) are presented herein, along with the typical damage observed. The causes of damage are qualitatively interpreted, wherever relevant evidence is available. To this purpose, the observed damage is compared to that occurred in other parts of the world, in structural systems similar to those of the area affected. Furthermore, the detrimental effect of inadequate pre-earthquake interventions is identified, while a critical discussion regarding frequently applied interventions, and the availability of design rules in current Codes and Guidelines, is initiated to pave the way toward efficient measures to be taken for the protection of surviving stone masonry buildings in Turkey and beyond.

Cyclic Behavior of Concrete-Filled Tube Columns with Bidirectional Moment Connections Considering the Local Slenderness Effect

In this research, the cyclic behavior of concrete-filled thin tube (CFTT) columns with bidirectional moment connections was numerically studied within the context of thin-walled structures. Novel considerations in the design of CFTT columns with slenderness sections are proposed through a parametric study. A total of 70 high-fidelity finite element (FE) models are developed using ANSYS software v2022 calibrated from experimental research using similar 3D joint configurations. Furthermore, a comparison of different width-to-thickness ratios in columns was considered. The results showed that the models with a high slenderness ratio reached a stable cyclic behavior until 0.03 rad of drift, and a flexural strength of 0.8 Mp was reached for 4% of the drift ratio according to the Seismic Provisions. However, this effect slightly decreased the strength and the dissipated energy of the moment connection in comparison to columns with a high ductility ratio. Moreover, an evaluation of concrete damages shows concrete cracked for cyclic loads higher than 3% of drift. Finally, the joint configurations studied can achieve a good performance, avoiding brittle failure mechanisms and ensuring the plastic hinges in the beams.

Effect of seismic provision on behaviour of steel and composite slab building analyzed using ETABs software

Effect of seismic provision on behaviour of steel and composite slab building analyzed using ETABs software

Comparison between the Dynamic Responses of Steel Buildings with Medium and Deep Columns under Several Seismic Intensities

Structural engineers often use deep columns in high seismic areas to reduce drifts, yet this somehow contradicts what is stated in some tests in the sense that even though deep columns may satisfy current seismic provisions, they can suffer premature twisting; this is an indication that a lot of research is needed in this area. Numerical and experimental studies have been conducted to estimate the response of steel buildings with medium and deep columns under the action of static and cyclic loading; however, studies accounting for the dynamic characteristics of buildings and strong motions are not common. In addition, responses in terms of local parameters have not been considered either. In this study, the nonlinear seismic responses of steel buildings with perimeter moment-resisting frames and medium (W14) columns are numerically calculated and compared to those of similar steel buildings with equivalent deep columns in terms of cost (W27 and larger). Low-, mid-, and high-rise steel building models with different dynamic characteristics, as well as several strong motions with different frequency contents, are considered. Results indicate that the drifts of the models with medium columns may be up to 140% greater than those of the models with deep columns. Significant reductions are also observed for top displacements, normalized interstory shears, and combined normalized axial loads and bending moments. Hence, the seismic demands of the buildings with deep columns may be much smaller than those of the buildings with medium columns and, therefore, the buildings with deep columns exhibit a superior behavior, which results in more economical designs. The reduction is greater for the case of low- and mid-rise buildings than for high-rise buildings. One of the reasons for this is that as medium columns are replaced by deep columns, the stiffness and the strength increase, which are lower in the tallest model.

Seismic performance of buildings during the magnitude 7.3 Kermanshah, Iran earthquake

In this paper, the findings and data of a large-scale reconnaissance mission following the November 12, 2017, M7.3 Kermanshah earthquake near the Iran-Iraq border are presented. The earthquake affected multiple cities in both countries and led to widespread damage and notable casualties and fatalities. The highest peak ground acceleration was recorded in Sarpol-e Zahab at 0.7g. As part of two trips, the data on nearly 1200 buildings in eight cities were collected by devising a sampling scheme to maximize the coverage of the survey, which was then employed to compile regional damage statistics. The spatial distribution of damage is presented for the entire region as well as various cities and neighborhoods in each city. The damage statistics are also disaggregated based on structural building, occupancies, and risk categories. The damage sustained by various categories of building components and contents is also assessed. In addition, the damage at the component level is closely examined for the structural and nonstructural components of severely damaged buildings to reveal the underlying causes that root in poor construction practices, lax enforcement of the building code, and inadequate seismic design provisions. Finally, the damage to hospitals in the region is investigated. This data, which can be augmented through a similar approach in the aftermath of probable future earthquakes, is key in calibrating the regional risk and resilience analysis of communities.

Evaluation of New Seismic provisions for special concentrically braced frames in AISC 341-22

The seismic provisions for special concentrically braced frame (SCBF) had expected the properly detailed braces to provide inelastic cyclic deformation of 10 - 20 ductility without fracture during the design earthquake ground motions over 30 years prior to 2022. The new seismic provisions for SCBF in AISC 341–22 eliminates the clear and quantifiable statements on the expected capacity and demand of the braces, and indicates that the diagonal braces can sustain large inelastic cyclic deformations without experiencing premature failures if they are properly detailed for ductility as prescribed in the provisions. The appearance of such word as “large inelastic deformation” and “premature failure” causes a concern about the uncertainty. One might wonder why a range of amount of inelastic cyclic deformation capacity for a properly detailed brace cannot be defined after more than 40 years of extensive research on SCBF. This paper presents a study using available data accumulated over more than 40 years to investigate how much inelastic cyclic deformations are needed for braces to avoid fracture under the design earthquake, and concludes that the SCBFs with properly detailed square HSS have insufficient inelastic cyclic deformations to avoid experiencing premature failures that lead to structural collapse under the design earthquake.

Evaluating and strengthening low-rise reinforced concrete buildings constructed in Nepal

In Nepal, the reinforced concrete (RC) frame system is commonly used to construct low-rise buildings. In last three decades, a significant number of such buildings were proportioned and constructed in accordance with Nepal National Building Code NBC 205:1994 and NBC 205:2012—also known as the Mandatory Rule of Thumb (MRT). In the aftermath of 2015 Gorkha Earthquake (Mw 7.8) which resulted in large scale social and economic losses, the efforts to formulate improved seismic design provisions led to the development of NBC 105:2020. Considering that MRT-designed low-rise RC frame buildings still constitute a significant part of existing building stock, this study is aimed to conduct a comparative seismic performance evaluation of several case study structures under a comprehensive set of ground motions. Using the nonlinear analysis and seismic fragility assessment of four low-rise RC frame buildings (designed using all three code versions), it is shown that the structural performance and seismic losses can be significantly reduced by following NBC 105:2020 provisions. Several retrofitting solutions are also explored to improve the seismic performance of buildings designed using MRT. It is shown that the concrete or steel jacketing of RC columns can significantly increase the lateral strength and energy dissipation, and reduce the damage probability of such buildings. Lastly, based on the developed results, a machine learning approach is employed to correlate the peak ground acceleration with structural drifts for convenient practical applications.

Canadian seismic design coefficients for coupled composite plate shear wall/concrete filled (CC-PSW/CF)

Concrete-filled coupled composite plate shear walls (also known as as SpeedCore walls) are gaining acceptance for construction in seismic region throughout North America. Design provisions for this lateral load-resisting system have already been added to ASCE 7-22 and to the American Institute of Steel Construction Seismic Design Provisions. Adequacy of the seismic design parameters used for this structural purpose has been validated in the USA using the FEMA P695 methodology. An interest was expressed by the practicing engineering community to use these walls in Canada, which requires demonstration of satisfactory seismic performance within the Canadian context. As such, new analyses are needed using Canadian-specific sets of ground motions to confirm the adequacy of the seismic design parameters proposed for implementation of these composite walls in the National Building Code of Canada. This paper presents the results of these analyses, showing that the proposed seismic performance factors are appropriate for this structural system in Canada.

Experimental and numerical investigation of through-diaphragm in H-shaped steel beam to CFST column connections

This research proposes a cruciform through-diaphragm (CTD) for an H-shaped steel beam to concrete-filled steel tubular (CFST) column and investigates its seismic performance experimentally and numerically. The proposed connection consists of through-plates passing through the aligned slots in the panel zone and end plates directly welded to an H-shaped steel beam. This connection eliminates welding inside the steel tube for installation of the diaphragm, while providing a reliable load path from the steel beam to the CFST column. The experimental program examined the connection hysteretic behaviors, including the moment-rotation response, ductility, initial stiffness, and energy dissipation capacity. The proposed connection shows stable hysteric behavior and good energy dissipation up to a story drift up to 4 % and satisfies the AISC seismic provisions criteria for special moment connection. A finite element (FE) model was established and verified against the experimental results. The effects of concrete infill, steel tube column thickness, axial load ratio, and through-plate thickness on the hysteretic behavior of the proposed connection were investigated through parametric analysis of 24 FE models. This study provides the information on the optimized design parameters that ensures the stable seismic performance of the proposed connection that could be used in structural engineering practice.

A Comparative Study of Seismic Performance Evaluation of Reinforced Concrete Frame Structures Using Chinese and African Seismic Codes

The evaluation of various earthquake codes, it is one of the significant challenges in the study area of earthquake engineering. However, according to the literature review, most research works have not addressed comparing Chinese and African seismic codes. Therefore, the purpose of this study is to identify each code’s advantages by comparing assessment of the seismic efficacy of moment resistance frame reinforced concrete (MRF-RC) frames using four different codes: the Ethiopian Building Code Standard (EBCS-8), the Egyptian Code for Design and Construction of Reinforced Concrete Structures (ECP-201), the Algerian Seismic Regulations (RPA-99), and the Chinese Code for Seismic Design of Buildings (GB-50011), the first three are the major codes used in Africa. The seismic provisions of these codes are compared and evaluated using nonlinear time-history analysis (NL-THA) and nonlinear static pushover to validate the results. These analyses are performed on four MRF-RC frame models with different heights. The results include various parameters that reflect the seismic performance of the structures. The study revealed that the Chinese code is more conservative and overestimates seismic performance compared with African codes. However, the Chinese code can be applied in African projects considering the African soil classifications, and seismic weight are adjusted to meet the African design criteria.

Effect of Seismic Design Provisions of Indian Standards on Seismic Response of URM Infilled RC Buildings on Hill

Effect of Seismic Design Provisions of Indian Standards on Seismic Response of URM Infilled RC Buildings on Hill

Seismic strengthening of isolated RC framed structures through orthogonal steel exoskeleton: Bidirectional non-linear analyses

The catastrophic effects of recent earthquakes around the world have highlighted the vulnerability of civil buildings; in Europe, most of the existing buildings were built after World War II and since they have largely exceeded their useful life, are characterized by a high vulnerability linked both to the durability of the materials and to the lack of seismic provisions in design. The current trend in constructional field is to design interventions aimed at the seismic and energy improvement of these structures jointly, in order to achieve a sustainable and integrated retrofit intervention. To this aim, the use of 2D orthogonal steel exoskeletons for the seismic strengthening represents a suitable solution, providing at the same time an enhancement in thermal insulation, through a ‘double-skin’ solution. Due to the growing interest in the design of steel exoskeleton interventions, a detailed dynamic characterization of this external strengthening solution is needed. In this framework, the present work, aims to investigate the effectiveness of the investigated strengthening solution by means of bi-directional non-linear dynamic analyses. Extensive numerical analysis was carried out. The selected case-study is an Italian existing pre-1980 s RC frame building located in Mugnano di Napoli (NA, Italy), which is a medium-high seismic hazard site in Italy (peak ground acceleration equal to 0.156 g). Two alternative strengthening solutions were numerically investigated by means of non-linear time-history and incremental dynamic analyses performed applying fifteen bidirectional ground motions on three-dimensional numerical models. The results of the dynamic non-linear analyses allow to quantify more appropriate performance indicators, both in terms of expected demand and overall collapse capacity, useful for the development of optimization strategy and design of exoskeleton system. The results highlighted that both the investigated strengthening scenarios allow to increase the stiffness of the existing building and allow it to meet the current code safety requirements reducing also the residual inter-storey drift. The obtained results are not strictly related to the investigated case study, but can be extended to all the structures retrofitted that follows the presented design procedure.

Numerical assessment of TMS 402/602-22 and CSA S304-14 seismic design provisions for partially grouted reinforced masonry shear walls failing in flexure

Despite the economic benefits of using partially grouted reinforced masonry shear walls (PG-RMSWs) as a seismic force resisting system (SFRS) in low-rise buildings, using such a system in mid- and high-rise buildings is still questionable. This is because the literature lacks comprehensive studies investigating different seismic design provisions adopted for rectangular and flanged PG-RMSWs of aspect ratios greater than 2.0 and failing in flexure. Therefore, this study aims to conduct a comprehensive numerical assessment of the seismic design provisions of the North American masonry standards (i.e., TMS 402/602–22 and CSA S304–14) for designing different categories of rectangular and flanged PG-RMSWs failing in flexure. In this regard, 108 PG-RMSWs were designed and modeled using the Extreme Loading for Structures (ELS) software. Afterward, some changes were proposed to the current seismic design provisions in CSA S304–14 and TMS 402/602–22 for rectangular and flanged PG-RMSWs. In addition, a comparison was made between the seismic design provisions for PG-RMSWs and FG-RMSWs, designed according to each RMSW category, to investigate the expected differences in the behavior based on the applied seismic design provisions. Accordingly, additional 36 FG-RMSWs were designed according to CSA S304–14 and TMS 402/602–22. These additional walls were then modeled on the ELS and compared with their PG counterparts. The results show that both standards can be safely used to design rectangular and flanged PG-RMSWs only when using the two proposed provisions for each standard. For CSA S304–14, the possibility of updating clause 16.8.5.2 is concluded, allowing the use of PG-RMSWs without limitations. New seismic force modification factors were also proposed for TMS 402/602–22 for the design of rectangular and flanged PG-RMSWs. Finally, the comparison between rectangular PG and FG-RMSWs failing in flexure and designed according to CSA S304–14 and TMS 402/602–22 shows that the behavior of PG-RMSWs failing in flexure is comparable to FG-RMSWs under certain circumstances. This study is considered a significant step to prove the potential for more economical and safe usage of PG-RMSWs in mid- and high-rise buildings.

Seismic Upgrade of an Existing Reinforced Concrete Building Using Steel Plate Shear Walls (SPSW)

Steel Plate Shear Walls (SPSW) provide significant lateral load capacity and can be utilized in the seismic retrofit and upgrade of existing reinforced concrete (r/c) buildings. In this study, the application of SPSW to retrofit a r/c building designed according to older seismic provisions is presented. Three different options to model SPSW are utilized, i.e., by equivalent braces, by finite elements, and by membrane elements, seeking not only to appropriately simulate the actual behavior of the SPSW but also to achieve the desired seismic behavior of the retrofitted building. Specific seismic response indices, including plastic hinge formations, are derived by non-linear time-history analyses in order to assess the seismic behavior of the retrofitted r/c building. Inspection of the results provided by non-linear analyses in conjunction with the different modeling options of the SPSW leads to the conclusion that the model with the membrane elements exhibits the best performance, implying that for the seismic retrofit and upgrade of existing r/c buildings, the use of membrane elements to model the SPSW is recommended.

Modeling and Prediction of Nonstationary Ground Motions as Time–Frequency Images

Proper modeling of nonstationary characteristics of ground motions is critical in estimating the seismic performance of structures. The importance of ground motion nonstationarity is being increasingly recognized in seismic design codes and provisions. This paper develops a new method for predicting seismic ground motions in the joint time–frequency domain based on recorded ground motions. We treat wavelet energy maps of acceleration records as images and extract essential patterns from them using principal component analysis. These patterns are then linked to the seismic source, path, and site variables using general regression neural network. The resulting model predicts an image representing the expected evolutionary power spectrum conditioned on the input variables. An example application is presented using records from the Next Generation Attenuation of Ground Motions Database of the Pacific Earthquake Engineering Center. As opposed to conventional ground motion prediction models, the proposed approach retains the time domain characteristics of ground motions. The results show that the proposed model can predict significant patterns in the seismic energy distribution, acceleration time series, and 5% damped elastic spectral accelerations.

Strong column-weak beam relationship of 3D steel joints with tubular columns: Assessment, Validation and Design proposal

The study of moment connections in steel structures subjected to cyclic loads has been extensively studied, providing a great number of requirements, including the strong column-weak beam relationship, to guarantee a satisfactory cyclic performance. However, investigations on the cyclic performance of moment connections considering the bidirectional and axial load effects simultaneously with tubular columns are limited. This study aims to assess and validate the strong column-weak beam relationship of 3D steel moment connections using reduced order models. The simplified model (reduced order model) approach was employed to extend the range of beam and column elements sizes and reduce the experimental and computational costs. These models were calibrated from full-scale experimental studies. A great number of configurations with different beam and column sizes without loss of reliability and structural representativeness of the studied phenomenon were studied. A total of 13640 simplified models were developed. Results show a cyclic behavior controlled by the strong column-weak beam relationship to modify the joint's failure mechanism. The increasing of strong column-weak beam relationship and the biaxial effect caused degradation of the strength and stiffness as well as in dissipated energy. An optimal strong column-weak beam relationship was obtained for all joint configurations analyzed. Finally, a robust design procedure is proposed, ensuring the cyclic behavior of end-plate moment connection with built-up box column including biaxial effect and axial load. Therefore, the use of this type of moment connection can be used in special and intermediate moment frames designed according to Seismic provisions.