Steel Braces Research Articles

Review on Fragility Analysis of Building Structure in Seismic Prone Area

In general, using a steel bracing system is the most effective choice for enhancing the resistance of reinforced concrete frames to lateral loads. Steel bracing offers notable advantages over other methods, including greater strength and stiffness, cost-effectiveness, a smaller footprint, and minimal additional weight on existing structures. Both empirical and analytical fragility curves have been taken into account. Strengthening seismically deficient reinforced concrete frames with steel bracing systems is a practical solution for improving earthquake resilience. Nearly all structural analysis software, such as ETABS and SAP2000, supports linear and nonlinear static analysis for high-rise structures. Key parameters include fragility curves, the P-Δ effect, base shear, lateral displacement, axial force, and story drift, among others. The findings showed that bracing systems significantly reduce lateral displacement in frames. Fragility curves were developed based on peak ground acceleration (PGA) for various limit states—slight, moderate, major, and collapse-assuming a lognormal distribution. This study aims to develop analytical fragility curves for high-rise building structures.

Evaluation of blast-induced progressive collapse in steel structures with conventional braces, moment-resisting braces, and buckling-restrained braces using LS-DYNA software

Today, considering the increased cases of terroristic operations, structural design engineers are starting to acknowledge blast-induced loads alongside other design parameters. Since a blast-induced load exhibits a much shorter period than the natural period of the structure, it is unlikely to induce general damages or stimulate the entire structure immediately after the loading, but rather local damages in individual structural elements are the common form of damage. These local damages, however, can set the scene for the gradual failure of the structure. The present study on structures with moment-resisting frames, buckling-restrained braces (BRBs), and conventional steel braces was conducted through an alternative load path (ALP, also known as column elimination) and exact modeling of the blast on the steel frames was undertaken using LS-DYNA software. In this work, the behavior of three five-story steel frames under a blast-induced load of 100 kg TNT equivalent at a distance of 10 m from the structural columns for a period of 100 ms was investigated. Results of analyzing the blast-induced effect on the frames showed that the frame equipped with buckling-restrained braces (BRB) exhibited improved overall peak displacement across the entire frame, peak induced velocity, and peak induced acceleration by 30%, 30%, and 46%, respectively, as compared to other steel frames exposed to blast loads.

Local and global integrative retrofitting of reinforced concrete frames using in‐plane buckling steel braces

AbstractTwo large‐scale, single‐storey, single‐bay reinforced concrete (RC) moment frames, designed as per an outdated seismic code to represent a typical framing detail of a four‐storey building, have been tested under displacement‐controlled quasi‐static loading protocol as per ACI 374.1‐05. The RC frames include a plinth beam with brick infill underneath, a slab monolithically cast with the top beam and provision for applying axial load to the column to simulate real construction scenario. One of the frames has been tested as a bare frame, and the second one has been retrofitted with conventional steel braces designed to undergo in‐plane buckling. The size of the brace has been selected based on the result of a nonlinear time history analysis of representative low‐ to mid‐rise open‐ground storey RC buildings. Post‐installed chemical anchors have been utilized to connect the steel braces to the narrow RC frame members following the outcomes of an experimental investigation by the same authors. Local‐level retrofitting by steel jacketing using adhesives has been designed and utilized on columns and beams to achieve the desired seismic response. The seismic performance of the retrofitted frame has been compared with the bare frame in terms of strength, stiffness, ductility, energy dissipation and hysteretic damping. The tests provide insight into the role of the plinth beam, effect of RC slab on the strong‐column weak‐beam aspect and the achievement of the desirable hinge mechanism through a precise design and detailing of global and local level retrofitting technique.

Development of Novel Buckling-Restrained Steel Braces Enabled by Partial Induction Hardening

Development of Novel Buckling-Restrained Steel Braces Enabled by Partial Induction Hardening

Fatigue and Ultimate Strength Evaluation of GFRP-Reinforced, Laterally-Restrained, Full-Depth Precast Deck Panels with Developed UHPFRC-Filled Transverse Closure Strips

A depth precast deck panel (FDDP) is one element of the prefabricated bridge element and systems (PBES) that allows for quick un-shored assembly of the bridge deck on-site as part of the accelerated bridge construction (ABC) technology. This paper investigates the structural response of full-depth precast deck panels (FDDPs) constructed with new construction materials and connection details. FDDP is cast with normal strength concrete (NSC) and reinforced with high modulus (HM) glass fiber reinforced polymer (GFRP) ribbed bars. The panel-to-girder V-shape connections use the shear pockets to accommodate the clustering of the shear connectors. A novel transverse connection between panels has been developed, featuring three distinct female-to-female joint configurations, each with 175-mm projected GFRP bars extending from the FDDP into the closure strip, complemented by a female vertical shear key and filled with cementitious materials. The ultra-high performance fiber reinforced concrete (UHPFRC) was selectively used to joint-fill the 200-mm transverse joint between adjacent precast panels and the shear pockets connecting the panels to the supporting girders to ensure full shear interaction. Two actual-size FDDP specimens for each type of the three developed joints were erected to perform fatigue tests under the footprint of the Canadian Highway Bridge Design Code (CHBDC) truck wheel loading. The FDDP had a 200-mm thickness, 2500-mm width, and 2400-mm length in traffic direction; the rest was over braced steel twin girders. Two types of fatigue test were performed: incremental variable amplitude fatigue (VAF) loading and constant amplitude fatigue (CAF) loading, followed by monotonically loading the slab ultimate-to-collapse. It was observed that fatigue test results showed that the ultimate capacity of the slab under VAF loading or after 4 million cycles of CAF exceeded the factored design wheel load specified in the CHBDC. Also, the punching shear failure mode was dominant in all the tested FDDP specimens.

Finite element analysis of square hollow section steel braces incorporating different infill materials under cyclic loading

Previous researches have extensively explored the use of concrete as an infill material for hollow steel sections, but there is limited reference on other types of infill materials.This study investigates the use of various infills, including wood, glulam, and H-beam, in square hollow steel braces to enhance buckling strength, widen stress concentration in the mid-span, and broaden the accumulation of plastic strain to delay local buckling and prolong the fracture cycle life of the brace. The proposed finite element method was utilized to assess the cyclic behavior of the braces, validated through three types of experimental tests on both unreinforced specimens and brace with infill material. An analysis was then conducted on 21 models to examine important parameters, such as section width-to-thickness ratio, flexural rigidity, filler length, and filler material. The results show that infill materials extend the von-Mises stress distribution at mid-span and reduce the PEEQ ratio. Additionally, the infill strengthens the buckling resistance of the brace; however, the effect of the infill does not significantly increase in models with lower width-to-thickness ratios. The infill also helps to improve the ductility ratio and energy dissipation capacity of the brace. From the fracture point of the hysteresis loop, the specimens with infill wood or glulam, as well as the specimens with shortened infill length, all demonstrate an ability to prolong the cycle life of the braces. Moreover, specimens with larger flexural rigidity of infill H-beam dramatically improve the fracture cycle life, which is also favorable for extending the life of the brace before rupture. However, it is recommended that the flexural stiffness ratio should be kept below a certain threshold to prevent buckling mechanisms in the transition zone.

Assessment of a Force Method for the Resilient Seismic Design of Special Moment-Resisting Steel Frames with Hysteretic Energy Dissipation Devices

In this paper, the authors present the results of nonlinear dynamic analyses of twelve building models designed according to a methodology based upon the force method, capacity design principles and the concept of structural fuses to achieve resilient seismic designs for special moment-resisting steel frames with hysteretic energy dissipation devices mounted on chevron steel bracing. It is demonstrated that the resilient design mechanism previously checked with pushover analyses is also attained for most studied models with nonlinear dynamic analyses using an acceleration record which is compatible with the elastic design spectrum. Also, it is corroborated that the planned second line of inelastic defense is activated if the seismic action surpasses the considered design spectrum. Based upon the obtained results, it is confirmed that it is possible to perform a resilient seismic design for the studied system under the proposed methodology, even for tall and slender buildings. Therefore, the proposed initial stiffness ratio parameters and the global design parameters previously proposed by the authors to use in a code-oriented force method can be used with confidence for the resilient seismic design of this structural system.

A new hold-down device for seismic applications in CLT buildings: Design, testing, analytical and numerical assessment

An hold-down device was designed and tested experimentally for seismic applications (Seismic Hold-Down, SHD). The magnitude of axial strength as well as the up-lift displacement capacity is mainly oriented to cross-laminated-timber (CLT) buildings with medium-to-high ductility. There is consensus in the design practice of hold-down devices for promoting, as dissipative mechanism, flexural yielding of the dowel-type connectors (e.g. nails, screws) combined to timber’s embedment. Few are the applications aiming at hold-down’s optimization as it emerges from up-to-date literature review. In this framework, SHD was conceived such that tension break-out of steel was promoted at a reduced segment (fuse) of the vertical flange. In the context of capacity design, a convenient overstrength was assumed for other failure mechanisms, e.g. anchor’s pullout, laterally-loaded steel-to-timber connection, shear-plug of timber. The mechanical response under axial load was consistently predicted by an application of the component method, i.e. global stiffness and strength were analytically-derived using simplified series of non-linear mechanical springs. Three-dimensional finite elements model was employed to investigate buckling of the fuse which might occur, during cycles, when up-lift displacement is recovering. In practical circumstances, it is recommend to design SHD devices of a CLT wall similarly to diagonal elements of steel bracings, i.e. neglecting the contribution of the compressed element. Finally, SHD is compared to traditionally-designed hold-down, which mostly dissipates (and fails) at steel-to-timber connection. Overall hysteretic response is somehow similar, although the inelastic mechanisms involved are different. For example, both the devices show pinching during cycles which for SHD is mainly caused by buckling of the fuse while, for traditional hold-down, is dominated by timber’s embedment.

Triple network hydrogel-based structure triboelectric nanogenerator for human motion detection and structural health monitoring

In this study, we developed a high-performance triple network (TN) PVA/PAAM/PEDOT/Zn2+ (PMPZ) hydrogel with exceptional mechanical properties and stable output performance. The robust and highly tough TN structure, fabricated via a Zn2+ pinned hydrogel and multi-network interpenetrating polymerization process, demonstrates high mechanical strength alongside exceptional mechanical properties. The PMPZ hydrogels exhibit notable mechanical sensing capabilities (gauge factor: 48.6) while maintaining excellent tensile (83.79 KPa) and compressive (96 MPa) strengths. As a triboelectric nanogenerator (TENG), the PMPZ-TENG shows outstanding flexibility and integrability, achieving a maximum open-circuit voltage (Voc) of 326.89 V and a peak power density of 368.3 μW/cm² with a load resistance of 10E8 Ω. Furthermore, the PMPZ-TENG demonstrates enduring practicality and responsiveness as a self-powered sensor. These properties make the PMPZ-TENG highly suitable for applications in human health monitoring. Additionally, we conducted computational simulations on the hydrogel and seismic-resistant civil models. 48 prototype structures simulated different seismic hazard levels to effectively capture plastic hinge deformation within high-strength steel composite K-shaped eccentric braced steel frames. The plastic hinge deformations informed the establishment of physical seismic models for structural health monitoring (SHM). This study not only introduces a high-performance PMPZ-TENG meeting practical requirements but also establishes a novel pathway for integrating TENGs in SHM.

Seismic performance of frame with middle partially encased composite brace and steel-hollow core partially encased composite spliced frame beam

Steel-hollow core partially encased composite spliced frame beam (SHSFB) and middle partially encased composite brace (MPECB) demonstrate the potential to economize on steel consumption while exhibiting superior performance. To investigate the seismic performance of frames with SHSFBs and MPECBs, horizontal low-cyclic loading tests were conducted on four frame specimens, involving two two-story frames with no brace and two multi-story X-braced frames. Numerical simulations were performed using the “Open System for Earthquake Engineering Simulation” (OpenSees). The results indicate that the novel composite frames exhibit commendable seismic performance and energy dissipation capacity. The unbraced frame with SHSFBs has deformation capacity and mechanical properties comparable to bare steel frame. In contrast to the frame specimen equipped with bare steel braces featuring a 6 mm flange thickness, the specimen utilizing MPECBs with 4 mm flange thickness exhibits only a slight reduction of 3.60 % in maximum bearing capacity and 2.68 % in initial lateral stiffness. Significantly, each SHSFB and MPECB component reduces steel consumption by 16.71 % and 24.79 %, respectively, compared to bare steel components. Therefore, while ensuring adequate mechanical properties, frame structures equipped with SHSFBs and MPECBs will require less steel. Based on both experimental and simulation results, the formulas for predicting the ultimate bearing capacity and initial lateral stiffness of the novel composite frame were proposed, and the structural design for the multi-story X-braced frame was analyzed, offering valuable insights for practical engineering applications.

Experiments and calculation methods on the tensile capacity of a single blind bolt anchored in a circular CFST section

Composite tubular joints that connect the steel brace and circular concrete-filled steel tubular (CFST) chords are crucial for the performance of entire composite truss structures. While welding is traditionally used for these connections, bolted connections offer an alternative in challenging environments where on-site welding is not feasible. The emergence of blind bolts provides an innovative solution for bolted CFST joints by offering bolted fastening without needing access to the inner surface of a closed section. This paper focuses on the tensile performance of a single blind bolt anchored in a circular CFST section. Experiments are conducted on three different configurations of blind bolts: non-anchored blind bolt with washer, anchored blind bolt without washer, and anchored blind bolt with washer. Based on the tests, the failure mode, the ultimate capacity, and the stiffness of the CFST-blind bolt specimens are investigated. The research findings show that the stiffness and ultimate capacity of the specimen are highly influenced by the bolt diameter, concrete strength, and effective embedment length, as well as the configuration of the blind bolt. And the effective embedment length has the most significant effect on the bearing capacity of the specimen. For every 30 mm increase in bolt effective embedment length, the bearing capacity of the specimen increases by at least 25 %. Finally, practical calculation methods are proposed to determine the ultimate capacity of CFST-blind bolt joints with various configurations under tensile action. The proposed calculation methods demonstrate high accuracy, as evidenced by the good agreement between the calculated values and experimental results.

Analysis of RCC Framed 45 Storey Building Using Different Combination of Outriggers

In this modern age of civil engineering, the construction industry has embraced a notable inclination towards erecting towering structures, with skyscrapers emerging as integral components of urban development. This trend presents a multifaceted challenge, not only for architects but also for structural engineers, who must ensure these high-rise edifices possess a robust design foundation capable of withstanding diverse loads and their combinations. While both wind and seismic forces exert significant pressures on tall buildings, the former often takes precedence due to its higher magnitude and frequency. Consequently, the structural design of high-rise buildings necessitates careful consideration of gravity, wind, and seismic loads. This study delves into the behaviour of reinforced concrete (RC) framed high-rise buildings (comprising 45 stories) augmented with outrigger truss systems constructed from both concrete and steel bracings. By exploring various configurations of outrigger placement, the aim is to mitigate structural deflection and compare the efficacy against conventional RC systems, both with and without shear walls.

Behaviour of Braced and Unbraced Multi-storey Steel Framed Buildings on Flat and Sloping Terrain

Behaviour of Braced and Unbraced Multi-storey Steel Framed Buildings on Flat and Sloping Terrain

Design-Optimization of Conventional Steel Structures for Realization of the Sustainable Development Objectives Using Metaheuristic Algorithm

The construction industry presents a significant environmental challenge due to its substantial environmental footprint, utilization of limited natural resources, and contribution to pollution and climate change. Additionally, optimizing the weight, cost, and duration of construction is crucial for enhancing serviceability, flexibility, efficiency, and profitability. In this research, the relationship between structure weight and other objective functions was explored using the single-objective gray wolf algorithm to investigate their impact on carbon footprint, water footprint, and construction time. Furthermore, employing a multi-objective optimization algorithm, a building structure was optimized for three systems featuring different structural frames based on the specified objective functions. The results revealed that the structure with intermediate steel moment-resisting frames exhibited the shortest construction time but incurred the highest construction cost. Conversely, the structure with intermediate steel moment-resisting frames with special steel concentric bracing demonstrated the lowest carbon footprint and water footprint among the studied structural frames. Consequently, the structure with intermediate steel moment-resisting frames with special concentric steel bracing was proposed as a green structure, emphasizing its environmentally friendly characteristics.

Optimizing Retrofit Strategies for RC Frames through Combined Techniques

Over the past twenty years, researchers have directed their efforts towards enhancing the earthquake resistance ofconcrete frames through repair and retrofitting. Two main approaches have emerged for bolstering the seismicresilience of previously intact structures prior to earthquake exposure. The first involves augmenting the existingstructure with additional components like steel bracing, while the second entails reinforcing specific structuralelements, such as employing steel cages. Seismic response analyses have been conducted on multi-story reinforcedconcrete (RC) frames originally designed without seismic considerations. This study aims to assess the effectiveness ofretrofitting techniques by comparing the outcomes of employing steel braces, steel cages, and their combinations. Theseismic performance is evaluated according to the RPA 2003 seismic code for Algeria, following the latest guidelines.Static nonlinear analysis was utilized to compare the seismic responses of existing non-ductile RC frames under variousretrofitting schemes.

Seismic Performance Evaluation of Steel Braces in Enhancing the Lateral Load Resistance of RCC Flat Slab Structures

This research paper conducts a comprehensive investigation into the seismic performance of reinforced concrete flat slab structures, employing different configurations of steel bracing systems. The seismic behavior of flat slab buildings with 5, 7, and 9 stories is scrutinized through Equivalent Lateral Force (ELF) analysis and Response Spectrum Analysis (RSA). The study delves into the efficacy of various bracing configurations, encompassing X-bracing, eccentric bracing, and knee bracing, in augmenting the lateral load resistance of these structures. Additionally, the research evaluates the influence of bracing systems on crucial structural response parameters such as displacement, drift ratio, base shear, and fundamental natural period. Keywords: steel bracing, seismic performance, flat slab structures, comparative study

Seismic fragility and loss assessment of standard/sub-standard RC frames of Pakistan retrofitted with steel bracing schemes

Seismic fragility and loss assessment of standard/sub-standard RC frames of Pakistan retrofitted with steel bracing schemes

Shaking table test and numerical analyses of a multi‐story traditional tower‐style building

AbstractThe traditional tower‐style building (TTSB) is an innovative structural form constructed in modern cities imitating the overall appearance of ancient timber pagodas, and it is an extraordinarily cultured high‐rise construction. The limited stipulations for high‐rise TTSBs in the seismic design code pose challenges in assessing the reliable performance of the unique structure subjected to severe earthquakes. This paper presents the shaking table test and numerical analyses of a 1/15‐scale 13‐story TTSB specimen with an integral tower height of 5.36 m, which is a steel frame‐braced core‐tube structure consisting of seven bright floors (built‐out stories evident from the outside, BF) and six dim floors (built‐in stories not apparent from the outside, DF), with transition columns and stiffening trusses around the exterior perimeter. The experimental results showed that the tested tower‐style building had excellent seismic performance and reliable structural integrity. It only experienced minor damage when subjected to extremely high‐intensity motions. The interstory drift, dynamic strain, and floor acceleration response of the core‐tube region with eccentric steel braces were more significant under severe excitation than those with cross‐centered symmetric steel braces. The vertical reaction increased at the upper floor of the tower under vertical acceleration, and differences in the dynamic response of the middle and upper floors were much more apparent after the test. Moreover, 3D numerical simulation models of the tested tower were established and validated against the test responses. Successively, the validated numerical model was used to investigate the influence of the transition column at different floors on the peak interstory drift response and the relevant strain distribution, and the proposal for a proper position of the transition column was recommended at the end.

ENHANCING STRENGTH OF EXISTING R.C.C. OVERHEAD WATER TANKS WITH Y TYPE STEEL BRACINGS UTILIZING NDT

Reinforcing of R.C.C. overhead tank greatly improved choice to upgrade the security and increment the existence time of design and furthermore it requires less economy and time. Steel bracing have demonstrated to give greater stability and sturdiness to any design. These bracing would bear both horizontal and vertical load in an exceptionally protected way. In this research, application of Y shapes steel bracing at every stage of RCC elevated Water tank was investigated to strengthen the model. Such bracing are generally used to strengthen the structure in high intensity seismic zones. This dissertation mirrors the utilization of non-destructive tests for appraisal of existing R.C.C. Overhead tank, trailed by examination through STAAD-Pro, with or without Y bracing to comprehend the impact of bracing on existing damaged R.C.C. Overhead Water Tank. Keywords: Staad.Pro, RCC water Tank, Y Bracing, Non Destructive Test (NDT).

Innovative Method for Reinforcing Beams with Different Types of Concrete Using Cross-Rod Steel Bracing Under Pure Torsion

This study aimed to investigate the effectiveness of an innovative way to reinforce the concrete beams using cross-rod steel bracing under pure torsion. The experimental program consists of casting and testing eighteen concrete beams made of three types of concrete in the form of three groups, with the same dimensions for all beams (200×200×2000) mm. The parameters of the study included concrete types (normal strength, high strength, and steel fiber), as well as the number of internally cross rods (4, 8, 12, 16, 20). The experimental results showed that the number of internally cross-rod reinforcements and concrete type had an effect on ultimate torque, crack width, toughness, and stiffness. The torsional capacity of all concrete beams increased with the increase in internally cross-rod reinforcement. The ultimate torque of normal-strength concrete beams, high-strength concrete beams, and steel fiber concrete beams reinforced with twenty internally cross rods increased (88.34%, 53.20%, and 40.60%), respectively, compared to beams without cross rods in each type of concrete beam. Increasing the internally cross rod in all concrete beams effectively inhibited the development of crack width and improved torsional stiffness, especially in fibrous concrete beams that contained steel fiber. The torsional toughness of all concrete beams increased with the increase of internally cross-rod reinforcement, and it was higher in steel fiber concrete beams. The steel fiber concrete beams reinforced with internally cross-rod steel bracing have better torsional properties compared to ordinary concrete beams and high-strength concrete beams. Doi: 10.28991/CEJ-2024-010-04-06 Full Text: PDF