Steel Braces Research Articles

Analytical Pushover Curves for X-Concentric Braced Steel Frames

In this work, analytical pushover curves for concentric braced steel frames with active tension diagonal bracings (X-CBF) are proposed. A pushover “spindle”, characterized by two trilinear analytical capacity curves defined for an X-CBF system subjected to prefixed lateral forces distribution, is defined. The curves are able to grasp the elasto-plastic behavior of the X-CBFs. The reliability of this analytical proposal is verified by a series of numerical comparisons obtained through an accurate finite element model, calibrated on the basis of experimental results. The proposal is extended to whole single- and multi-storey structures, showing a good correspondence with the numerical results of the analyzed case studies.

Comparative study of Multistoried Building with X & Inverted V Bracing

The most suitable technique in order to increase the performance and the lateral stability of the RC Frame building situated in earthquake prone areas is the use of steel bracings. In this paper comparison of seismic behavior of G+15 multistoried building situated in zone 4 on medium soil has been carried out on 3 different models by installing different types of bracing i.e X bracing and inverted V bracing. The designed structure should have enough lateral stability in order to resist the lateral force during the seismic shaking, and the parameters such as the storey drift should be within the permissible limits as per the IS 1893-2016. The use of Steel Bracing in Reinforced concrete structure not only helps to reduce the lateral loads during the earthquake but also helps us to reduce the section size of the reinforced concrete structures. In this paper 3 models have been analysed- Model no 1 – G+15 building without steel bracing, Model no 2- G+15 building with X bracing, Model no 3 – G+15 building with inverted V bracing, All the 3 models have been analysed with the help of STAAD PRO V8i software and comparison between these models have been carried out based on 3 seismic parameters such as Storey Drift, Storey Displacement and Base shear. Keywords Storey Drift, Storey Displacement, Base Shear, Seismic Analysis, Steel Bracing.

Prediction and forewarning of axial force of steel bracing in foundation pit based on verhulst model.

The axial force of steel bracing is one of the essential indexes to measure the stability of the bracing system of a foundation pit. The steel bracing system of a foundation pit in Ningbo City, China was taken as the research object to guarantee the stability of the steel bracing system of the foundation pit. Besides, the change of axial force between the two steel bracing structures was analyzed to predict the axial force data of the steel bracing and perform the safety forewarning of the steel bracing system. Firstly, GM (1,1) and Verhulst models in the gray model were selected for prediction based on the characteristics of poor information and the small sample size of original monitoring data of the steel bracing. Secondly, the precision of the GM (1,1) model and Verhulst model was compared to determine a more accurate prediction method. Finally, the safety forewarning model of the confidence interval estimation method was established based on the data obtained from the prediction model and the deformation characteristics and indexes of the steel bracing. With the significance levels α = 5% and α = 2% as the demarcating points, the forewarning grades of the steel bracing system of the deep foundation pit were divided, and then the operating state of the current steel bracing system was determined. The results demonstrated that the Verhulst model had better prediction precision compared with the ordinary GM (1, 1) model. Besides, the steel bracing system was in the safe operation range, and the judgment results of the model were consistent with the actual situation of the foundation pit of the steel bracing system. Thus, the Verhulst prediction model and the confidence interval security early forewarning model could be used to judge the stability of the steel bracing system.

Recent progress in buckling restrained braces: A review on material development and selection

Passive energy dissipation devices are a widely accepted solution used to improve the response of the structures under seismic conditions. While several types of passive energy dissipation elements have been proposed for replaceable elements, buckling restrained braces (BRB) was one of the most effective replaceable elements which has been used to retrofit frame structures in the past few years. A traditional BRB consists of a steel brace core with a cruciform cross section that is surrounded by a stiff steel tube (restraining unit) and unbonded materials to ensure the brace to move freely. The region between the tube and brace is filled with concrete-like materials. In recent years, a significant amount of research has been carried out on new types of BRBs which are more efficient and inexpensive. This paper presents an overview of recent advances in the development of BRB materials and buckling mechanism, with an emphasis on the material development for the restraining unit. The application of fibre-reinforced polymer (FRP) as restraining unit in BRB is highlighted.

Component testing and multi-level seismic design of steel braced frames with high post-yielding stiffness and two-phase yielding

Using induction heat (IH) treatment to locally transform one half of a steel brace section to high-strength steel section as well as inducing intentional eccentricity along the brace length has been experimentally proven to increase the limited post-yielding stiffness exhibited by conventional steel braces. This paper develops a multi-level seismic design method for intentionally eccentric IH-treated steel braced frames (IH-FIEB) to support their implementation in building structures. More specifically, experimental results on the cyclic behaviour of IH-treated steel braces with intentionally eccentricity (IH-BIEs) are presented giving an emphasis in quantifying member's resistance to local buckling and fracture initiation. A theoretical model is developed on the force-deformation relationship of the bracing system which is validated with test results and results obtained from a parametric finite element analysis study. On the basis of theoretical model, design expressions that describe the mechanical two-phase yielding behaviour of the bracing system controlled by the alternated flexural-axial behaviour are developed. The high post-yielding stiffness and controllability of the brace response through eccentricity provide the brace the capability of satisfying multiple strength performance objectives simultaneously. Time-history analysis results under three seismic hazard levels demonstrate that IH-FIEBs assure a more uniform overstrength and plastic engagement between each story than the conventional steel braced frames. IH-BIEs smoothly transition into post-buckling response and engage plastically at low drift demands, while seismic forces developed are well controlled and close to the values expected from the design procedure. A significant reduction of the residual deformation is observed at high seismic intensity levels indicating that IH-FIEBs may be able to reduce post-hazard damage compared to conventional braced frames.

Development of Vibration Control Structure on Suspended Ceiling Using Pulley Mechanism

A suspended ceiling system (SCS) is one of the most fragile and non-structural elements during earthquakes. However, effective seismic protection technologies for enhancing the suspended ceiling system have not been developed other than the steel bracing system. An innovative passive vibration control system is proposed in this paper, which equipped a damper-employed pulley amplification mechanism into the indirect suspended ceiling system, named the pulley–damper ceiling system (PDCS). Theoretical formulation and the detailed information on the system were presented first. In addition, a new rotational damper composition consisting of a non-linear viscous damper was developed to follow the large wire-cable stroke. Six types of the full-scale ceiling specimens of a 15.6-square meter area with different configurations were constructed for the preliminary experiments to evaluate the seismic performance and feasibility of PDCS under simulated earthquake motions. The comparative results of the shake table test demonstrated that the application of PDCS is capable of controlling both displacement and acceleration of the ceiling panels. This study also presents the nonlinear time history analyses by modeling a wire-cable as an equivalent truss element to transmit the relative displacement of the ceiling system to the damper. The analytical model accurately simulated the dynamic behavior of PDCS.

Design of X-Concentric Braced Steel Frame Systems Using an Equivalent Stiffness in a Modal Elastic Analysis

In this work, a general method for the design of concentric braced steel frames (CBF) with active tension diagonal bracings, applicable to single- and multi-storey structures, is presented. The method is based on the use of an elastic modal analysis with a response spectrum, which is carried out using an appropriate modified elastic stiffness of diagonal bracings. The reliability of the proposed method is validated through the analysis of significant case studies, making a series of numerical comparisons carrying out time-history non-linear dynamic analysis.

Hybrid self-centering rocking core system with fiction spring and viscous dampers for seismic resilience

This research presents a novel aseismic system, the hybrid self-centering rocking core (HSRC) system, for obtaining better seismic resilience in steel buildings. Two hybrid self-centering dampers are introduced in the HSRC system to control structural and nonstructural damage. A rocking core, i.e., a steel braced frame with pinned base is included in the HSRC system to facilitate uniform inter-story drift responses under earthquakes. The steel braces in the rocking core can also work as a reserve energy-absorbing mechanism against structural collapse subjected to extreme seismic events whose intensities are more significant than those of the maximum considered earthquakes in design codes. The desired nonlinear responses of the HSRC system were analyzed. Direct displacement-based design steps were developed for the HSRC system. Three-story and six-story HSRC systems were designed following the proposed design method. Nonlinear dynamic analysis results indicate that the designed HSRC systems can show desired nonlinear responses and achieve the expected performance objective under earthquakes. Moreover, seismic fragility analyses were also conducted based on the incremental dynamic analysis results to assess the performance in controlling structural and nonstructural damages of the HSRC system under earthquakes of different intensities. The results confirm that the proposed HSRC system has excellent capacity in resisting structural collapse, achieving reliable post-earthquake recoverability, and controlling structural and nonstructural damage under rare seismic events.

Development, simulation, and validation of sliding self-centering steel brace with NiTi SMA wires

This study proposes an innovative sliding self-centering (SC) brace to reduce or eliminate residual deformation after strong earthquakes. The brace uses tension-only nickel and titanium (NiTi) shape-memory alloy wires to generate SC behavior and tension-only steel bars to provide energy dissipation, axial strength, and axial stiffness. The proposed sliding SC brace concept and details are outlined, and tests are conducted on variations of the proposed brace subject to cyclic loading to investigate their hysteretic behavior. The experimental results demonstrated that the proposed brace exhibited a double-flag-shaped hysteretic response, controlled axial strength, and preferable SC behavior. An important advantage is that the tension-only steel bars of the proposed brace exhibit a sliding hysteretic response, which can significantly reduce the number of NiTi shape-memory alloy wires and decrease the cost of the brace. The proposed sliding SC brace mechanisms and governing equations for practical engineering designs are presented. A cyclic restoring force model with a trilinear skeleton curve, which reflected the sliding characteristics and SC features, was proposed and calibrated using experimental results. Additionally, the finite element analysis results were aligned with the test results. Three main design parameters affecting the sliding SC brace energy dissipation and SC ability are addressed.

Seismic performance of buckling-restrained braced steel frames subjected to earthquake main shock-aftershock sequences

Recently, there are many papers report the development of some new buckling-restrained braced (BRB) frames and the evaluation of its characteristics. At the same time self-centering buckling-restrained braced (SCBRB) frames are considered as new solutions for the increasing of the structural resilience. In this thesis, the seismic performance of structures is analyzed subjected to earthquake main shock-aftershock sequences. There is comparison of two types of the additional BRB elements, and also there is comparison between them and original steel frame to show the effect of using BRB and SCBRB elements. To compare the seismic performance of BRBF and SCBRBF, the same main shock-aftershock sequences were used in this part. Because of the flag-shaped hysteretic curve of the SCBRB elements, big amount of the energy was dissipated during the motion. Compared to steel frame, smaller seismic responses and residual deformation occurred the structure. BRBF and SCBRBF can control the seismic responses effectively due to the energy dissipation of BRB, and SCBRB can also reduce the structural residual deformation. The earthquake aftershock after earthquake main shock can increase the structural damage and enlarge the structural seismic responses.

Seismic Performance of RC Split-Foundation Frame Structures with Steel Braces in the Mountainous Area

Reinforced concrete (RC) split-foundation frame structures are widely used in mountainous areas. There are two grounding terminals with different heights in the split-foundation frame structures. Under the earthquake, the local damage phenomenon of the structures is severe due to the uneven stiffness distribution. It is one way to improve the seismic performance of the split-foundation frame structures to install steel braces in the upper embedding floor. According to the deformation characteristics of the upper embedding floor, three types of steel braces arrangement for the split-foundation frame structures were proposed: horizontal braces, V-type braces, and V-[Formula: see text] braces. Then based on the ratio of lateral stiffness of steel braces and concrete frame columns, the section of steel brace was designed. A quasi-static test was carried out to analyze the influence of steel braces on the failure mode of the RC split-foundation frame. The reasonable seismic waves were selected to carry out the nonlinear dynamic time history analysis. Then the seismic response and failure mode of the split-foundation frame structures with different braces arrangements were compared. On this basis, fragility analysis was carried out, and the earthquake-induced collapse resistance capacity of split-foundation frame structures with steel braces was preliminarily evaluated. The results show that the horizontal steel brace can improve the phenomenon of damage concentration of the split-foundation frame structures. Furthermore, setting V-shaped braces can significantly reduce the damage degree of the upper embedding end columns and change the phenomenon of locally severe damage of the split-foundation frame structures. Moreover, according to the design method proposed in this paper, setting steel braces can improve the seismic collapse resistance capacity of the split-foundation frame structures.

Experimental and numerical analyses of seismic behavior of concrete shear wall with opening accompanied by steel frame and eccentric encased steel braces

Reinforced concrete shear walls with the steel reinforced concrete frames is a common lateral force resisting structural system that is applied high-rise steel buildings in various forms. In this study, seismic behavior of two reinforced concrete (RC) shear walls with openings accompanied by steel reinforced concrete (SRC) on scale of 1/3 were investigated. One of the shear walls consisted of a steel truss reinforced concrete (STRC) with a specified eccentricity in each story level and its end was connected to the bracing’s steel beam. Both of the shear walls were coincidentally subjected to specific constant gravity load and cyclic load. Behavior assessment of shear walls included determination of the failure mode cracking pattern, loading capacity, strength, stiffness and dissipated energy with respect to generated deformations. Results revealed that the shear wall with encased steel brace (ESB) was more effective in terms of all the mentioned parameters compared to SRC wall. In the following, pushover curves for shear walls were investigated using finite element (FE) models and confidentiality of analytical models and prediction of behavior of these walls were verified based on real prototypes. Finally, effects of axial gravity load variations on FE models of both shear walls were evaluated. This study can be useful in applied structural engineering because of applying eccentric braces in openings of a reinforced composite shear wall.

Behavior of Reinforced Concrete Frames Retrofitted by Different Configurations of Concentric Steel Braces

Behavior of Reinforced Concrete Frames Retrofitted by Different Configurations of Concentric Steel Braces

Assessment of specific structural and ground-improvement seismic retrofitting techniques for a case study RC building by means of a multi-criteria evaluation

Existing reinforced concrete (RC) structures might not comply with current seismic codes due to their aseismic design and construction date. By seismically retrofitting them, it is possible to improve their seismic performance to resist the expected seismic loads. However, selecting the best solution is challenging since social and economic issues can affect the choice. Multi-criteria decision making (MCDM) provides an opportunity to overcome the challenge but there are some drawbacks in the available MCDM techniques. This paper reports an improved MCDM-based seismic retrofit: Additional criteria have been included and weighted according to their importance (ductility improvement and damage reduction); Finite element modelling of the case study building has been carried out instead of following methods based on different simplifications; iii) Structural performances have been assessed by determining the damage in local elements instead of following global assessment procedures; Effects of soil-structure interaction (SSI) have been taken into account to ultimately compare different structural and ground-improvement techniques. Consistency and sensitivity analyses have proved the stability of the results and the robustness of the method. It is shown that SSI can increase the seismic damage up to 17%, and regarding the seismic safety verification, the building needs to be retrofitted. Adding fibre reinforcement polymers and steel bracings are the best solutions due to the minimum architectural impact and the outstanding structural improvement, respectively. Nevertheless, the solution preferred is the addition of single steel braces in beam-column joints despite its high maintenance costs. The sensitivity analysis indicates that the most sensitive criteria are the functional compatibility and the reduction of the collapse risk.

Ocjena ponašanja i prijedlog pojačanja postojeće građevine

Due to major-scale earthquakes, revisions of earthquake resistant structural design methods have periodically been made in seismic codes. It is known that many existing buildings are located in active seismic zones in all parts of the world. Severe damage to structural members, with partial or total collapse of buildings, has been observed in past earthquakes. Consequently, the evaluation of seismic performance and strengthening techniques of the existing buildings according to various seismic codes has become a global issue in structural engineering. With the development of computer technology, non-linear methods have been offering increasingly reliable evaluation procedures in the performance-based assessment of buildings. In this study, non-linear performance analysis of an existing typical mid-rise reinforced concrete building is first performed according to Turkish Building Earthquake Code-2018 and American Standard, ASCE. After evaluation of damage to structural members, the building is strengthened by steel braces and the analysis is performed once again. The SAP2000 finite elements analysis software is utilized in the solutions. Damage ratios of structural members as well as modal properties and storey drift ratios are determined and compared according to both codes, and it is concluded that the proposed strengthening method could be a significant alternative in such buildings.

Numerical Analysis of Multilevel Eccentric Chevron Braced Frame for Improved Inelastic Behavior

AbstractThis paper presents a renovation strategy to upgrade the conventionally constructed chevron braced (both concentric and eccentric) steel frames in such a way that each set of the upgraded b...

DETERMINATION OF LOCATION AND NUMBER OF BRACES FROM TOWER CRANE TO CONSTRUCTION BUILDING

This study focuses on the performance of tower crane considering the brace from the basic tower to the building. Using specialized Finite Element Method (FEM) software to calculate and design steel structure of tower crane; determining the number and erection position of steel braces from the basic tower to the building. Thereby, assessing the safety level as well as the working ability of the tower crane. Then make comments, reviews and suggestions for similar structures.

Utilization of motion capture systems for low cycle fatigue tests on induction-hardened steel

Motion capture systems were used to control the low cycle fatigue test of heated and unheated specimens obtained from induction-hardened curved steel braces. The two motion capture systems used in this study demonstrated that the axial-strain control was achieved, and the strain distributions were visualized using digital image correlation. Additionally, the test results demonstrated that the fatigue lives of the unheated and heated specimens can be predicted using Manson's universal slopes method. However, the obtained fatigue lives were slightly shorter. Induction hardening proved to be an effective method to increase the fatigue life of specimens subjected to small strain.

Failure modes of bonded wrapped composite joints for steel circular hollow sections in ultimate load experiments

The concept of an innovative bonded joining technology where welding is not required is presented as an alternative to traditional welded connection for steel circular hollow section (CHS). Wrapped composite joints have potential to greatly improve fatigue endurance when applied in multi-membered truss structures, e.g. offshore jackets for wind turbines. This paper focuses on characterization of resistance and understanding of failure modes of wrapped composite joints in static experiments, as the prerequisite for harvesting its potential for high fatigue endurance. Wrapped composite joints at two scales and with two different angles of X-joint geometry are made with GFRP composite material wrapped around steel sections without welding, and tested in 3 monotonic loading cases, tensile, compression and in-plane bending, until failure. Counterpart welded joints are tested at the smaller scale for stiffness, elastic limit and ultimate load comparisons. Two general failure modes of wrapped composite joints, debonding and fracture of the composite material are identified and quantified by surface strain measurements through 3D digital image correlation (DIC) technique. Testing results indicate that wrapped composite joints have 30% to 56% larger stiffness and 3% to 68% larger ultimate load compared to welded counterparts. Debonding and final pull-out of steel brace member from the composite wrap is predominant failure mode in tensile experiments at both scales while cracking of the composite material is the governing failure mode in the bending experiment. In tensile, compressive and bending experiments failure load of wrapped composite joints exceeds the yield resistance of the steel CHS indicating opportunity to optimize the composite wrapping thickness and length.

Linear dynamic analysis of high-rise irregular structures with or without LFRS & frictional damper

This study categorically assists in describing the behavior of Irregular structures consist of G + 20 Storey through linear dynamic analysis for seismic assessment of structures. Linear dynamic analysis or response spectrum analysis helps us to evaluate the several parameters in respect of severe responses in irregular structures. At the time of design, A well analyzed structure shows which fragile part of structure needs to give an attention at the time of design to resist and dissipate the energy of seismic force occur on a structur3e during the earthquake. Response spectrum analysis is a seismic analysis method, which shows the response of structure when a seismic load taken into an account. In this study series of sequential response spectrum analysis of High-rise irregular structures have compared with the similar structures after assigning shear walls, Steel bracings and Frictional dampers respectively, and simultaneously all the purposed structure responses have compared with a regular structure accordingly with same consideration of lateral force resisting system. The complete modelling and analysis have done by the prominent analytical FEM integrated software “ETABS” in the seismic zone IV by considering relevant data for the particular seismic zone by IS 1893 (Part-1) 2016. All the reinforcement criteria for the components of structure has been taken into consideration as per suggested by IS 13920 for the ductile design. The response parameter aims for structures due to seismic loading are in terms of Max. displacement, Storey shear. Ultimately, it was concluded that the shear wall is more desirable than the other for reducing the max. displacement with the average reduction percentage of 61.33%.