Ductile Response Research Articles

Finite Element Modeling and Analysis of Perforated Steel Members under Blast Loading

Perforated steel members (PSMs) are now frequently used in building construction due to their beneficial features, including their proven blast-resistance abilities. To safeguard against structural failures from explosions and terrorist threats, perforated steel beams (PSBs) and perforated steel columns (PSCs) offer a viable alternative to traditional steel members. This is attributed to their impressive energy absorption potential, a result of their combined high strength and ductile behavior. In this study, numerical examinations of damage assessment under the combined effects of gravity and blast loads are carried out to mimic real-world scenarios of external explosions close to steel structures. The damage assessment for PSBs and PSCs considers not just the initial deformation from the blast, but also takes into account the residual capacities to formulate dependable damage metrics post-explosion. Comprehensive explicit finite element (FE) analyses are performed with the LSDYNA software. The FE model, when compared against test results, aligns well across all resistance phases, from bending and softening to tension membrane regions. This validated numerical model offers a viable alternative to laboratory experiments for predicting the dynamic resistance of PSBs and PSCs. Moreover, it is advisable to use fully integrated solid elements, featuring eight integration points on the element surface, in the FE models for accurate predictions of PSBs’ and PSCs’ behavior under blast loading. A parametric study is presented to investigate the effect of web-opening shapes, retrofitting, and different blast scenarios. The results obtained from the analytical FE approaches are used to obtain the ductile responses of PSMs, and are considered an important key in comparisons among the studied cases.

Advancing seismic resilience: Performance-based assessment of mid-rise and high-rise engineered cementitious composite (ECC) Buildings

Engineering Cementitious Composites (ECC) have received wide attention in recent years due to their enhanced mechanical properties and ductility. These properties offer an opportunity to design structures with significantly improved seismic performance having a low-damage and ductile response. However, existing research studies primarily focus on the performance of ECC at material and member scales, resulting in a knowledge gap regarding its response at the structural level. This study examines the system-level seismic response of buildings designed using ECC and compares their performance with those having conventional reinforced concrete (RC) members. For this purpose, two RC shear wall buildings (7-story and 24-story) were selected as a case study, and their elements were separately designed (for the combined gravity and lateral loads) as RC and ECC elements using the guidelines recommended by the Japan Society of Civil Engineering (JSCE) and ACI (American Concrete Institute)−318–19. The design results show that the requirement of longitudinal steel is reduced by a maximum of 24% in ECC flexural members and by 15% in compression members, in addition to a significant reduction in the required transverse reinforcement as compared to the corresponding RC members. Similarly, owing to improved tensile behavior, the ECC members also exhibited a higher shear capacity than RC members. The detailed nonlinear finite element models of the case study buildings (for both the design cases i.e., ECC and RC) were subjected to monotonic and reversed-cyclic pushover analysis, and nonlinear time history analyses (NLTHA) under a set of selected ground motions. It was observed that ECC structures exhibited significantly improved lateral capacity, revered-cyclic response, and overall seismic performance as compared to the corresponding RC structures. These results demonstrate that ECC can be effectively used to design various members for improved seismic performance of buildings.

Cyclic Behavior of the Column-Tree Moment Connection with Weakened Plates: A Numerical Approach

The use of column-tree connections is common in controlled shop environments due to their cost-effectiveness in achieving ductile welds. Field bolts are also easy to install and inspect. However, there is currently no prequalification available for these connections, their performance is not fully understood, and the cost of aftermath repairs is still a major concern for owners. In this research, analytical and numerical studies were performed to assess the cyclic behavior considering the effects of the bolted splice location, bolt slippage, and splice plate thickness. Fourteen numerical models using the finite element method in ANSYS software were analyzed to evaluate the nonlinear behavior of moment connection configurations in terms of the strength, stiffness, ductility, energy dissipation, and overall cyclic response. The results showed that appropriately proportioned bolted splice connections can meet the requirements for prequalified moment connections. The models complied with the criteria established in AISC 358 and achieved flexural resistance that was higher than 80% of the beam plastic moment at 4% of the interstory drift ratio. The weakened plates concentrated the inelastic action, which allowed us to prevent the brittle behavior and damage to the column, welding, and other components of the moment connection. Complex geometries or specially fabricated parts were not required, providing a cost-effective way to control seismic-related damage. Also, required repairs are based on the replacement of standard parts, reducing operational detentions in facilities. Finally, the moment connection studied is classified as partially restrained (PR) according to the requirements established in AISC 360.

Multiscale study of enhancing the fracture properties of interfacial transition zone: Insights from molecular dynamics and finite element simulations

Cementitious composites are widely used in architecture and construction field, but usually show quasi-brittle failure at macroscale under tensile or bending loads. In contrast, the calcium silicate hydrates (C-S-H) exhibits noticeable ductile response at nanoscale. In this article, we focus on the interfacial transition zone between cement paste and aggregate, which consists of the C-S-H/quartz and the calcium hydroxide (CH)/quartz interface structures. To comprehend how a nanoscale design might improve concrete’s macro mechanical qualities, molecular dynamics and finite element simulations are performed at the nanoscale and macroscale, respectively. The elastic properties, modulus, fracture toughness and critical energy release rate of C-S-H/CH/graphene oxide (GO)/quartz composites are calculated using the molecular dynamics method at nanoscale. These parameters then are used in macro-simulation and calculating mechanical properties of macro concrete structures. The incorporation of GO sheets into the interface results in a 38.40% to 58.06% increase in the fracture toughness of interfacial transition zone (ITZ) systems and an 80% and 9.81% improvement in the tensile strength and tensile modulus of the concrete model, respectively. This fundamental insight into nanoscale interfaces notably allows for more accurate predictions of macroscopic mechanical behavior, paving the way for innovative and enhanced cement-based materials in the future.

Experimental and analytical studies of size effects on compressive ductility response of Ultra-High-Performance Fiber-Reinforced concrete

Ultra-high-performance fiber-reinforced concrete (UHPFRC) has gained a great deal of increasing interest in structural engineering applications, particularly where high ductility, strength, and high impact resistance are of prime concern. This study focuses primarily on the size effects ductility characteristics of UHPFRC with varying fiber concentrations subjected to uniaxial compressive load. It shows how to process the data from compression cylinder tests to extract the size-dependent strain at peak stress to provide a generic size-dependent stress–strain analytical model. For a slenderness factor of 2, the predicted peak stress from the analytical model deviated 0.34%, 0.26%, and 10.5% from the experimental peak stress results for a fiber concentration of 1%, 2%, and 3%, respectively, indicating good estimate of the analytical model with the experimental results. Furthermore, a numerical flexural segmental moment-rotation approach is applied to incorporate an analytical model to quantify apparently disparate UHPFRC member strength and ductility. Tests have shown that it is not the enhancement in the material concrete compressive strength but the phenomenal brittle ductility nature, observed as a result of increasing the slenderness of the specimen; in contrast, a substantial increase in ductility was achieved after crushing of concrete due to the addition of fibers. A size-dependent analytical approach has estimated good fit with the experimental and other published results. Finally, numerical simulation using a segmental approach at the ultimate limit state of rotation dealing with flexural ductility is significantly influenced by the increase in slenderness factor of the specimens and fiber concentrations.This is evident as the rotation capacity decreased by 62% and 75% for a slenderness factor of 3 and 4, respectively, compared to the slenderness factor 2, when the fiber concentration was 1%. Furthermore, for 2% fiber concentration, the decrease was 54%, and 80%, and for 3% fiber concentration, the decrease was found to be 49%, and 79% for the slenderness factor of 3 and 4, respectively in comparison to the slenderness factor 2, suggesting both slenderness factor and fiber concentration have a significant impact on the flexural ductility.

Axial compression behaviour of concrete filled double skin steel tube columns anchored with orbicular rings: Experimental and numerical approach

Double-skin tube column sections have been used extensively in recent years. These sections are composed of two adjacent, coaxially spaced steel casings, and the space in the middle of them is occupied with concrete. These CFDST columns behave similarly to CFST sections but are more rigid and have a lesser self-weight. The behavior of a novel type of CFDST column, the orbicular anchored CFDST column, was assessed under axial compression in the current research. It comprises an inside and an outside steel tube with orbicular rings near the ends of the columns. The orbicular rings were positioned at various spots such as [Formula: see text] and [Formula: see text] and a wide range of tests were accomplished to evaluate the functionality of orbicular anchored CFDST columns in respect of maximum load-bearing capability, load-strain behavior, and load-deformation behavior. A FE model was developed and its accuracy was authenticated by comparing its findings with experimental results. Furthermore, a parametric investigation was carried out employing the authenticated FE model to examine the functioning of the proposed CFDST to variations in orbicular position, cross-sectional dimensions of rings, yield strength of orbicular ring, etc. The outcomes of the study indicated that orbicular anchored CFDST columns had 15% higher ultimate load capacity than unstiffened counterparts. The orbicular anchorage improved the ductile response and increased the axial stiffness of the CFDST column. Further, it was concluded that orbicular rings enhanced the constraining effect of external steel casing on sandwiched concrete and improved the composite action of CFDST specimens. The design formula to ascertain the load-bearing ability of columns was also developed and can be employed amid preliminary designs of proposed column sections.

Inter-void shearing effect on damage evolution under plane strain deformation in high-strength aluminum alloy sheet

In this study, the ductile damage responses of high-strength 7000 series aluminum alloy (AA), AA 7075-T6 sheet samples, subjected to the plane strain deformation mode were investigated using finite element (FE) simulations. In the experiments, uniaxial tension (UT) and plane strain tension (PST) tests were conducted to characterize the plasticity and ductile damage behavior of the AA 7075-T6 sheet samples. The limiting dome height (LDH) and V-die air bending tests were conducted to evaluate the ductility of the material subjected to plastic deformation and friction between the tools, and the corresponding fractured samples were qualitatively analyzed in terms of dimples using fractography. FE simulations were performed to predict the ductility of the AA 7075-T6 sheet samples under plane strain deformation using an enhanced Gurson−Tvergaard−Needleman (GTN) model, namely the GTN-shear model. The model was improved by adding the shear dimple effect to the original GTN model. The predicted results in terms of the load–displacement curves and displacements at the onset of failure were in good agreement with experimental data from the aforementioned tests. Furthermore, virtual roll forming simulations were conducted using the GTN-shear model to determine the effect of the prediction on ductile behavior for industrial applications.

Full‐Scale Steel Moment‐Resisting Frame with Dissipative Bolted Connections under Monotonic Loads: Experimental versus Numerical Results

AbstractIn the light of the new National Annex in Germany (DIN‐EN‐1998‐1/NA), in which extended seismic areas and higher spectral accelerations are specified, dissipative design of steel structures gains significance for moderate seismic regions as well. The use of the inherent ductility of steel can lead to an effective and safe design. Thus, a series of beam‐to‐column joints with dissipative bolted connections for Moment‐Resisting Frames were developed within an ongoing German‐funded project. The aim is to develop joint typologies, which can dissipate energy through a ductile response of the connection. Joints from the German catalogue of typical connections were used as a starting point. They were investigated and improved using FE numerical simulations to exclude brittle failure and provide dissipative, semi‐rigid and partial‐strength beam‐to‐column joints, which could allow for the use of behaviour factors in the range 1.5÷3. The optimized joints were used within full‐scale frame specimens (10.0 m length, 3.0 m height) and tested under monotonic and cyclic loads. The paper provides an overview of the: ▪ experimental program; ▪ monotonic test results; ▪ numerical results of the calibrated numerical model, as well as the response of the beam‐to‐column joints; ▪ main conclusions.

Influence of anchored orbicular rings on the performance of sandwich concrete‐filled double‐skin steel tube columns

AbstractSince recent years, double‐skin tube column sections formed from two parallel, concentrically spaced steel casings, with the sandwiched area between the casings packed with concrete infill, have been employed extensively. The cross‐sectional shapes of the inner and outer casings might be the same or different, such as round, square, octagonal, etc. These concrete‐filled double‐skin steel tubular (CFDST) columns act similarly to concrete‐filled steel tubular (CFST) sections but have less self‐weight and better stiffness. The present study evaluated the response of CFDST column stiffened with orbicular rings under axial compression. It consists of inner and outer steel tubes stiffened by orbicular rings near both ends of columns. The orbicular rings were provided at different locations as L/3, L/4, and L/5, and a series of tests were conducted to obtain the performance of CFDST columns stiffened with orbicular rings with regard to the maximum load‐carrying capacity, load–strain behavior, and load‐deformation behavior. Furthermore, a parametric study was conducted by varying the diameter to thickness ratio, hollowness ratio, the thickness of orbicular rings, yield strength, and location of orbicular rings. The results showed that CFDST column stiffened with orbicular rings have higher ultimate load capacity than unstiffened CFDST. Stiffened CFDST with orbicular rings showed more ductile response than CFDST column and helps to improve the outer steel tube's restraint on sandwiched concrete. In order to estimate the load‐bearing capacity of CFDST columns stiffened with orbicular rings under axial compression, an empirical equation was proposed. The experimental results and findings of the suggested equations were found to be in good agreement.

Constitutive model for plain and fiber‐reinforced lightweight concrete under compression

AbstractIn this research work, experimental investigations of the compressive behavior of plain and fiber‐reinforced lightweight‐aggregate concrete have been carried out (this formed part of a wider study, which also examined tensile and flexural behaviors). Compression mechanical properties were established in the studies and a generic constitutive compressive σ–ε model for both plain and fibrous lightweight concrete was derived and validated against experimental results from the present studies and previous research in the literature involving different types of lightweight aggregates, concrete strengths, and steel fibers. The reliability of predictions of the constitutive model was also checked against existing fibrous concrete models. A fiber‐reinforcing factor was also introduced taking into account the fiber volume fraction, fiber length and diameter, the number of fiber bends, and concrete compressive strength. As such, this was considered a better descriptor of the material than simply using the fiber volume fraction. The lightweight aggregates examined in the experimental study were recycled from fly ash waste and the fibers were hooked‐ended with single, double, and triple bends (corresponding to DRAMIX steel fibers 3D, 4D, and 5D types, respectively). The fibers were added at volume fractions Vf of 1% and 2% and the experimental studies were carried out using standard cube and cylinder uniaxial compression test specimens. It was concluded that the higher the number of bends and fiber content, the more pronounced the enhancement provided by the fibers to the compressive strength and ductility responses. All steel fibers used in the present studies were found to significantly improve the compressive toughness, while only 4D and 5D fibers (i.e., those with double and triple end bends) enhanced the compressive strength by up to 12% and 15%, respectively. It was also found that the elastic properties of plain lightweight concrete remained unaffected by the addition of fibers.

Evaluation of Factors Affecting the Performance of Fiber-Reinforced Subgrade Soil Characteristics Under Cyclic Loading

This study is focused on evaluating the factors affecting the performance of fiber-reinforced subgrade under cyclic loading. To achieve the objectives of this study, a series of dynamic triaxial (DT) tests was performed, and the following parameters, such as resilient modulus (MR), number of loading cycles (N), cyclic stress (CS), resilient strain (RS), and stress-strain hysteresis response of both the reinforced and unreinforced subgrades were evaluated. Subsequently, a series of scanning electron microscope (SEM) tests was conducted to track the fiber-soil interfacial bonding after the completion of DT test. The results indicated that N and CS triggered an appreciable decrease in MR with significantly high RS deformation for the unreinforced subgrade. However, reversed responses were noted upon the inclusion of sisal fiber due to fiber-soil adhesion and a high ductility response was portrayed by the reinforced subgrades. A reversed response was significant upon 0.25% and 0.5% fiber inclusion, beyond which the CS resistance slightly decreased. The stress-strain hysteresis loop was observed to increase as the axial strain increased proportionally with an increase in fiber contents, thus causing a significant increase in energy absorption in specimens. The SEM micrograph showed tightly knitted fiber-soil adhesion after the DT test. This study indicated that the reinforced subgrade sustained the CS, N, and improved energy absorption capacity, and MRupon fiber inclusion. Doi: 10.28991/CEJ-2023-09-08-015 Full Text: PDF

Punching Shear Behavior of FRP Grid-Reinforced Ultra-High Performance Concrete Slabs

Fiber-reinforced polymer (FRP) grid-reinforced ultra-high performance concrete (UHPC) slabs are new structural solutions that take advantage of the mechanical properties of FRP and UHPC. However, the punching shear behavior of this new slab type has not been characterized. Therefore, punching shear tests were conducted to eight carbon fiber-reinforced polymer (CFRP) bars or grid-reinforced UHPC square slabs (600 mm side width × 40 mm thick). Several influential factors [e.g., use of CFRP bars or grids as flexural reinforcements, type of strengthening short fiber, steel fiber (SF) content, and presence of shear reinforcements] were investigated. The test results showed that FRP grids and short fibers helped to distribute the applied loads and dissipate the input energy; therefore, more cracks were observed, and higher punching shear capacities were achieved. Furthermore, increasing the reinforcement ratio in the FRP grids led to a more significant postcrack ductility response, which increased the punching shear capacity by 17%. In addition, SF addition could enhance the initial cracking load of the slab (Vcr), and polyethylene (PE) fiber addition could intensify the postcrack ductility response, both enhanced the punching shear capacity. The installation of shear reinforcements (eight pieces of 80 mm long CFRP grid strips) appeared to be more cost-effective than increasing SF content. Finally, compared with the current design provisions for conventional reinforced concrete slabs, a more accurate (average error of 8%) punching shear model was proposed for FRP grid-reinforced UHPC slabs with or without SF additions. However, the robustness of the proposed model will be assessed with more test data in the future.

Seismic response of CFST Double-Tee moment connections: Design criteria and experimental tests

The unsymmetric prying response of the T-stub flange of Double-Tee connections with Concrete-Filled-Steel-Tube and Through-Bolts (CFST-TB) is investigated in the present article. A design method is presented and discussed to enhance the ductility of the connections accounting for the Unsymmetric Prying Action (UPA) and the longitudinal strain of the through bolts. Two joints have been alternatively designed in accordance with AISC-358 and the proposed rules and also tested to evaluate and compare their performance and failure mode. Finite element models have been validated against the experimental results and finite element simulations have been carried out to assess the local response of the considered joints. The results indicated that the performance of the AISC358-compliant specimen was affected by through-bolt fracture and damages to the T-stub segment at the first cycle of 0.04 rad interstory drift angle. The UPA-compliant specimen had a satisfactory performance without any damage to the connection components until 0.06 rad interstory drift angle. Therefore, experimental and numerical results showed that the proposed criteria can guarantee an effective and ductile response of CFST-TB Double-Tee connections.

Seismic behavior of concentric and eccentric New-RCS through-beam joints

Composite frame structures with high-strength reinforced concrete columns (New RC) and steel beams (S) are called New RCS systems. The key to the development of the New RCS system is the development of beam-column joint details. Thus, in this study, four large-scale beam-column subassembly specimens: three interior joint specimens, and one exterior joint specimen, were designed and cyclically tested to investigate the seismic behavior of the New RCS joint. Two tested interior joint specimens had beams framing to the New RC column with eccentricities, while the other specimens had concentrically framing beams. All the specimens exhibited stable and ductile hysteretic responses. The experimental study showed that the proposed joint details could develop the desirable beam flexural yielding while limiting joint damage for drift levels up to 6%. However, at very high drift levels (≥ 6%), the overstrength of the highly compact cross-section of the steel beams of the test specimens resulted in significant joint damage for the interior joint specimens. The experimental study demonstrated that the proposed New RCS joints were able to accommodate eccentrically framing beams without hampering the seismic response.

Analysis of RC Multistory Building with and Without Blast Forces

Blast resistant and anti-terrorism design is essential in order to save the civil infrastructure and human lives. In the design of structures, a consideration for energy absorbing capabilities to resist the effects of blast loading or other severe dynamic loads it is vital, and structural provision of elements with large plastic deformation capacities is desirable. Structures need to be designed for ductile response in order to prevent partial or total collapse due to locally failed elements. The work in this paper considers theoretical studies to resist the structure against blast loading to understand the basic concept of explosion phenomena, parameters of blast loading, and different types of blast waves. The analysis focuses on the estimation of blast loading on structures and their response to explosions. Design of blast resistant structures requires thorough understanding of the structural dynamics, behaviour of materials under high strain rate of loading, and blast analysis. This paper concludes with an explanation of findings by different researchers using different country codes to simplify the design process for calculating blast load. Keywords: Blast Resistant Design, Blast Load, Explosion, ETABS.

Strength, Ductility, and Collapse Response of UHPC Waffle Slabs

Waffle slabs made of ultra-high performance concrete (UHPC) are now being widely used in bridge deck construction. However, to date, no research has been conducted to study their failure behavior. Two one-way waffle slab strips made of UHPC were load-tested under four-point bending to investigate their strength, ductility, and failure patterns. An identical set made of high strength concrete (HSC) was also tested to provide a comparison to specimens made with traditional construction materials. The UHPC specimens exhibited multiple fine cracks prior to rebar yielding and failed by steel rebar rupture after a single crack localized. In contrast, the HSC slab strips exhibited several large cracks and substantially larger ductility than the UHPC slab strips, although their strength was about 40% less than the corresponding UHPC specimens. The experimental results were used to validate a three-dimensional finite element model, which was then employed to investigate the two-way response of UHPC waffle slabs. The simulation study revealed that the yield line design method is applicable to UHPC waffle slabs despite their markedly different behavior compared to concrete slabs. Like the HSC slabs, the UHPC slabs also exhibited displacements and load carrying capacities well in excess of those predicted by flexural theories, due to formation of membrane action.

Tensile behaviors of stainless steel anchor channel systems embedded in concrete: Experimental and numerical analyses

Stainless steel anchor channels with channel bolts (SSAC-CBs) are extensively used in reinforced concrete structures subjected to corrosive environments owing to the excellent heat and corrosion resistance, appreciable inelastic deformation capacity, and high ductility of stainless steel. However, limited tests and numerical simulations have been conducted describing the tensile behaviors of SSAC-CB assemblies. We therefore conducted static monotonic tension tests to investigate the structural behaviors of SSAC-CBs embedded in concrete in terms of failure mode, tensile load-bearing capacity, ductility, and plastic development response. The test variables included the anchor/channel profile type, stainless steel grade, and tensile load position. The SSAC-CB specimens exhibited three dominant failure modes in tension: combined yielding of the channel lips and webs, flexural deformation of the channel, and concrete splitting. The ductility ratios of the test specimens ranged from 4.56 to 8.45, indicating a significant inelastic deformation capacity. Based on the maximum tensile loads obtained in the experiments, the ultimate limit state principle was employed to recommend tensile design resistances according to anchor channel type. In addition, nonlinear finite element analysis models were constructed in ABAQUS using three-dimensional solid elements to facilitate detailed investigations of the tensile behaviors of SSAC-CBs embedded in concrete; the numerically obtained failure modes and loads agreed well with the experimental responses. Finally, the experimental data were applied to propose and validate analytical expressions for the tensile load-bearing capacities of SSAC-CBs embedded in concrete corresponding to their different failure modes under tensile load.

Seismic pre-qualification tests of EC8-compliant external extended stiffened end-plate beam-to-column joints

An experimental and numerical campaign was carried out to validate the design procedure and prequalify extended stiffened end-plate (ESEP) joints for ductile seismic resistant moment-resisting frames in the framework of Eurocodes. In fact, the tested ESEP joints have been designed with the aim of guaranteeing ductile and dissipative seismic response in accordance with the principles of the hierarchy of resistances to enforce plastic deformations in ductile components of the joints. Two alternative types of dissipation mechanisms are promoted, namely either (i) plastic deformations solely in the connected beam using full strength joints or (ii) plastic deformations in both the beam and the connection using equal strength joints. The adopted design criteria and technological details are described and discussed. The results of experimental tests confirmed the expected yielding mechanisms of the joints, which satisfied the acceptance criteria for both North American and European prequalification. Finite element simulations of ESEP joints have been validated against the experimental results and have been used to investigate the local response of the joints, thus highlighting the influence of both geometrical and mechanical parameters.

Creep–fatigue mechanical characteristics of salt rocks under triaxial loading: An experimental study

Salt rock is a sedimentary rock that is widely distributed in the crust. Since salt rock has a low permeability, rheological behavior, and self-healing characteristics, it has been extensively exploited for subsurface energy storage and waste disposal. The construction of compressed air energy storage (CAES) facilities using salt caverns for solution mining is a practical solution to achieve carbon peaking and carbon neutrality goals worldwide. The stability of the salt cavern surrounding rock is critical to the function of a CAES plant. Considering the triaxial stress condition of the rock surrounding such underground salt caverns, a number of triaxial creep–fatigue mechanics tests were performed on salt rock using an MTS815 mechanical testing device. The creep–fatigue damage to the salt rock was examined under various confining pressures and stress levels. The main research results and conclusions are as follows. First, the triaxial creep–fatigue stress–strain curves show a similar tendency to classical triaxial fatigue results: the strength and ultimate deformation of salt rocks increase as the confining pressure increases. Second, in contrast to typical fatigue test results, the residual strain before the high-stress plateaus is larger than that after the plateaus during a creep–fatigue test. However, as the confining pressure increases, this disparity decreases. Third, fatigue loading increases creep deformation, and this effect weakens when the confining pressure increases. Fourth, the residual strain differential before and after the high-stress plateau increases together with the stress level, and the contribution of creep strain increases correspondingly. Last, as the confining pressure increases, the salt rock behavior transitions from a brittle response to a fully ductile response. A high confining pressure prevents relative sliding between the salt rock particles. Thus, the effect of confining pressure on the creep–fatigue mechanical behavior of the salt rock reaches a threshold.

Kahramanmaraş—Gaziantep, Türkiye Mw 7.8 Earthquake on 6 February 2023: Strong Ground Motion and Building Response Estimations

The effects on structures of the earthquake with the magnitude of 7.8 on the Richter scale (moment magnitude scale) that took place in Pazarcık, Kahramanmaraş, Türkiye at 04:17 a.m. local time (01:17 UTC) on 6 February 2023, are investigated by processing suitable seismic records using the open-source software OpenSeismoMatlab. The earthquake had a maximum Mercalli intensity of XI (Extreme) and it was followed by a Mw 7.5 earthquake nine hours later, centered 95 km to the north–northeast from the first. Peak and cumulative seismic measures as well as elastic response spectra, constant ductility (or isoductile) response spectra, and incremental dynamic analysis curves were calculated for two representative earthquake records of the main event. Furthermore, the acceleration response spectra of a large set of records were compared to the acceleration design spectrum of the Turkish seismic code. Based on the study, it is concluded that the structures were overloaded far beyond their normal design levels. This, in combination with considerable vertical seismic components, was a contributing factor towards the collapse of many buildings in the region. Modifications of the Turkish seismic code are required so that higher spectral acceleration values can be prescribed, especially in earthquake-prone regions.