Experimental and numerical study of buckling-restrained braces configured with out-of-plane eccentricity under cyclic loading

This study focuses on variations in the hysteretic behavior of buckling-restrained braces(BRBs)configured with or without out-of-plane eccentricity under cyclic loading.Quasi-static experiments and numerical simulations were carried out on concentrically and eccentrically loaded BRB specimens to investigate the mechanical properties,energy dissipation performance,stress distribution,and high-order deformation pattern.The experimental and numerical results showed that compared to the concentrically loaded BRBs,the stiffness,yield force,cumulated plastic ductility(CPD)coefficient,equivalent viscous damping coefficient and energy dissipation decreased,and the yield displacement and compression strength adjustment factor increased for the eccentrically loaded BRBs.With the existence of the out-of-plane eccentricity,the initial yield position changes from the yield segment to the junction between the yield segment and transition segment under a tensile load,while the initial high-order buckling pattern changes from a first-order C-shape to a secondorder S-shape under a compressive load.

Development and subassemblage cyclic testing of hybrid buckling-restrained steel braces

Buckling-restrained braced frames(BRBFs) are vulnerable to relatively higher post-earthquake residual drifts under high intensity ground shakings. This is primarily due to the low axial elastic and post-elastic stiffness of bucklingrestrained braces(BRBs) satisfying the design force demand requirements. In the present study, a hybrid buckling restrained bracing system consisting of a short yielding core length BRB component and a conventional buckling-type brace component connected in series has been developed with an aim to increase the axial stiffness of braces. This study is focused on the experimental investigation of six hybrid bucking restrained braces(HBRBs) to investigate their overall behavior, loadresisting capacity, strength-adjustment factors and energy dissipation potential. The main parameters varied are the crosssectional area, the yielding length of core elements as well as the detailing of buckling-restraining system of short yielding core length BRBs. Test results showed that the HBRBs with yielding core length in the range of 30% of work-point to workpoint lengths withstood an axial strain of 6% without any instability and can deliver stable and balanced hysteretic response and excellent energy dissipation under reversed cyclic loading conditions.

Application of buckling-restrained braces in the seismic control of suspension bridges

Buckling-restrained braces(BRBs)are widely used to improve the seismic performance of buildings.This paper aims to introduce BRBs to suspension bridges and assess the seismic performance of bridges with BRBs.Taking the Dadu River Bridge as a case study,an FEA model of the bridge is established,and different seismic measures(BRBs between the deck and the tower,BRBs at the middle of the span to replace the inclined suspenders to connect the deck and the main cables,fluid viscous dampers(FVDs)between the deck and the tower,the combination of BRBs to replace the inclined suspenders as well as FVDs between the deck and the tower)are applied to the suspension bridge.The influence of the parameters of BRBs on the seismic response of the suspension bridge is studied,and the performance of the bridge with BRBs is compared with that of the bridge with FVDs.The results indicate that the use of BRBs in place of the inclined suspenders is beneficial to reduce the displacement of the deck and limit the shear force and bending moment of the tower.The seismic performance of the suspension bridge with BRBs and FVDs is better than that of the bridge with BRBs or FVDs.Therefore,the application of BRBs is a feasible method to improve the seismic performance of the suspension bridge.

Seismic performance of a reinforced concrete building retrofitted with self-centering shape memory alloy braces

Self-centering earthquake-resistant structures have received increased attention due to their ability to reduce post-earthquake residual deformations and,thus,repair time and cost.This stimulated the development of recentering shape memory alloy(SMA)dampers that use superelastic nitinol wires to dissipate energy and self-center the structure.However,there are still a few case studies applications on full-scale RC buildings in the literature.Moreover,general guidelines or even simplified approaches for the practical design of SMA damped braces are still lacking.This paper focuses on evaluating the effect of using self-centering shape memory alloy dampers for buckling-restrained braces applied for the seismic retrofit of a complex RC building structure.A design method originally proposed for elastoplastic dampers was implemented to size the SMA dampers to be placed on selected spans and stories of a building.The effectiveness of the design procedure was demonstrated by nonlinear time-history analyses under different sets of earthquake strong ground motions.The analysis results show that the recentering shape memory alloy bracing system is effective in limiting the maximum transient inter-story drifts and reducing the residual inter-story drifts after strong seismic events,due to its excellent recentering behavior together with its not negligible energy dissipation capacity.

Use of Crescent Shaped Braces for Controlled Seismic Design of Ductile Structures

It is known that the seismic response of a structural system is highly influenced, in addition to the earthquake input, by the dynamic characteristics of the system itself. This paper presents an approach for the identification of the characteristics of the structural system resisting to horizontal loads which enables to satisfy given seismic performance objectives. This is achieved by considering a total conceptual separation between the structural systems resisting to vertical and horizontal loads. The proposed approach is first briefly developed in general within a Performance-Based Seismic Design （PBSD） framework and then fully applied to the case study of a five-storey steel building structure. It is composed of three basic steps： （1） identification of the fundamental characteristics which should be possessed by the horizontal resisting system to satisfy a multiplicity of performance objectives, （2） development of a peculiar horizontal resisting system composed of ＂crescent shaped braces＂ which are specifically calibrated to satisfy given performance objectives, （3） verification, by means of appropriate time-history analyses, of the seismic performances achieved. In detail, the horizontal resisting system is calibrated to satisfy a multiplicity of performance objectives through the identification of an ＂objectives curve＂, in the Force-Displacement diagram, of the mechanical characteristics of the structure. The calibration is obtained by methods/tools borrowed either from Direct Displacement-Based Design （DDBD） or Force-Based Design （FBD）, depending on the specific performance objective to be imposed. The applicative example has been carried out with reference to three performance objectives and has led to the identification of a horizontal resisting system composed of special bracing elements capable of realizing a sort of properly-calibrated seismic isolation called crescent-shaped braces. The results obtained through non-linear dynamic analyses have shown that the proposed approach leads to the congruity between the imposed and the achieved seismic performances.

Seismic Response of Reinforced Concrete Buildings Retrofitted with Dissipative Steel Braces

The present work discusses the outcomes of recent experimental tests and numerical simulations carried out on full scale reinforced concrete （RC） non-ductile frames retrofitted with dissipative steel braces, i.e. innovative buckling restrained braces （BRBs）. Experimental tests were performed on two sample full scale RC framed buildings designed for gravity loads only. Such frames were subjected to cyclic pushovers to investigate their structural performance under different levels of earthquake loadings. The outcomes of the performed experimental tests demonstrate the efficiency and reliability of utilizing BRBs to retrofit non ductile RC frames. These outcomes were confirmed by refined non linear static and response history analyses carried out on an existing RC school framed building designed without seismic details and retrofitted with BRBs similar to those adopted for the tested full-scale frame. In such sample building the BRBs are placed along the perimeter of the existing frames to minimize the interruption of the functionality of the school and for easy of maintenance in the aftermath of major earthquake ground motions. The seismic performance assessment of the retrofitted structural system is illustrated in a detailed manner. Local and global response quantities are presented. The values of the global overstrength Ω for the case study vary between 2.14 and 2.54 for the retrofitted framed building. The translation ductility μ△-values range between 2.07 and 2.36. The response modification factor （or behaviour factor, namely R- or q-factor） is on average equal to 5.0. Additionally, the estimated maximum axial ductility of the BRBs is about 10. Finally, the cost-effectiveness of the adopted retrofitting scheme is emphasized and further needs for the application of BRBs are highlighted.

Design of Dissipative Braces for an Existing Strategic Building with a Pushover Based Procedure

The research presented in this paper deals with the seismic protection of existing frame structures by means of passive energy dissipation. An iterative displacement-based procedure, based on capacity spectrum, to design dissipative bracings for seismic retrofitting of the frame structures is described, and some applications are discussed. The procedure can be used with any typology of dissipative device and for different performance targets. In this work, the procedure has been applied, with both traditional pushover （load profile proportional to first mode） and multimodal pushover, to an existing RC （reinforced concrete） frame building. In the application, the buckling restrained braces have been used in order to prevent damages to both the structure and non structural elements. The use of multimodal pushover proves to be more effective than pushover based on single mode in case of medium rise RC frame building （higher than 30 m） but, once this building is retrofitted, and therefore regularized, with a bracing system, the difference between using monomodal or multimodal pushover becomes insignificant.

Nuss procedure for the correction of pectus excavatum by using double braces in adolescence

Objective To investigate the indication,feasibility and technique of minimally invasive Nuss procedure with thoracoscope by using double braces in the treatment of wide-scope pectus excavatum repairing in adolescence. Methods 31 patients including 24 boys and 7 girls,suffered from pectus excavtum were corrected by Nuss procedure under thoracoscope. The average age

Mathematical modeling and full-scale shaking table tests for multi-curve buckling restrained braces

Buckling restrained braces （BRBs） have been widely applied in seismic mitigation since they were introduced in the 1970s. However, traditional BRBs have several disadvantages caused by using a steel tube to envelope the mortar to prevent the core plate from buckling, such as： complex interfaces between the materials used, uncertain precision, and time consumption during the manufacturing processes. In this study, a new device called the multi-curve buckling restrained brace （MC-BRB） is proposed to overcome these disadvantages. The new device consists of a core plate with multiple neck portions assembled to form multiple energy dissipation segments, and the enlarged segment, lateral support elements and constraining elements to prevent the BRB from buckling. The enlarged segment located in the middle of the core plate can be welded to the lateral support and constraining elements to increase buckling resistance and to prevent them from sliding during earthquakes. Component tests and a series of shaking table tests on a full-scale steel structure equipped with MC-BRBs were carried out to investigate the behavior and capability of this new BRB design for seismic mitigation. The experimental results illustrate that the MC-BRB possesses a stable mechanical behavior under cyclic loadings and provides good protection to structures during earthquakes. Also, a mathematical model has been developed to simulate the mechanical characteristics of BRBs.

Do ankle braces provide similar effects on ankle biomechanical variables in subjects with and without chronic ankle instability during landing?

Purpose:The purpose of this study was to examine effects of a sport version of a semi-rigid ankle brace (ElementTM) and a soft ankle brace (ASO) on ankle biomechanics and ground reaction forces (GRFs) during a drop landing activity in subjects with chronic ankle instability (CAI)compared to healthy subjects with no history of CAI.Methods:Ten healthy subjects and 10 subjects who had multiple ankle sprains participated in the study as the control and unstable subjects,respectively.The CAI subjects were age,body mass index and gender matched with the control subjects.The arch index and ankle functions of the subjects were measured in a subject screening session.During the biomechanical test session,participants performed five trials of drop landing from 0.6 m,wearing no brace ( NB),ElementTM brace and ASO brace.Simultaneous recording of three-dimensional kinematic (240 Hz)and GRF (1200 Hz) data were performed.Results:The CAI subjects had lower ankle functional survey scores.The arch index and deformity results showed greater arch deformity of ElementTM against a static load than in NB and ASO due to greater initial arch position held by the brace.CAI participants had greater eversion velocity than healthy coutrols.The ASO brace reduced the first peak vertical GRF whereas ElementTM increased 2nd peak vertical GRF.ElementTM brace reduced eversion range of motion (ROM) and peak eversion velocity compared to NB and ASO.In addition,ElementTM reduced dorsiflexion ROM and increased peak plantarflexion moment compared to NB and ASO.Conclusion:Results of static arch measurements and dynamic ankle motion suggest that the restrictions offered by both braces are in part due to more dorsiflexed ankle positions at contact,and higher initial arch position and stiffer ankle for ElementTM.

Seismic retrofitting of reinforced concrete frame structures using GFRP-tube-confined-concrete composite braces

This paper presents a new type of structural bracing intended for seismic retrofitting use in framed structures. This special composite brace, termed glass-fiber-reinforced-polymer （GFRP）-tube-confined-concrete composite brace, is comprised of concrete confined by a GFRP tube and an inner steel core for energy dissipation. Together with a contribution from the GFRP-tube confined concrete, the composite brace shows a substantially increased stiffness to control story drift, which is often a preferred feature in seismic retrofitting. An analysis model is established and implemented in a general finite element analysis program - OpenSees, for simulating the load-displacement behavior of the composite brace. Using this model, a parametric study of the hysteretic behavior （energy dissipation, stiffness, ductility and strength） of the composite brace was conducted under static cyclic loading and it was found that the area ratio of steel core to concrete has the greatest influence among all the parameters considered. To demonstrate the application of the composite brace in seismic retrofitting, a three-story nonductile reinforced concrete （RC） frame structure was retrofitted with the composite braces. Pushover analysis and nonlinear time-history analyses of the retrofitted RC frame structure was performed by employing a suite of 20 strong ground motion earthquake records. The analysis results show that the composite braces can effectively reduce the peak seismic responses of the RC frame structure without significantly increasing the base shear demand.

Behavior of double K-BRB braces under lateral loading

The buckling resisting brace(BRB)is an efficient system against lateral loads that enjoy high seismic energy absorption capacity.Although desirable behavior of BRBs has been confirmed,the stiffness of the system is not desirable that it can be compensated by changing the configuration of BRB braces.In so doing,the configuration in the form of double K(DK)is investigated to achieve more favorable behavior.Also,the required mathematical formulas were proposed to design the system.Comparison of DK system with other conventional BRB showed that the DK system has a better structural performance and is more economical(due to needing less core area)than other conventional BRB.Numerical results indicated that the DK system increases the lateral ultimate strength,lateral nonlinear stiffness,and energy absorption.Besides,the DK configuration reduces the axial forces created in columns in the nonlinear zone.Reducing material demand,created forces in the main frame,and also increasing of nonlinear stiffens by DK improve the structure’s safety.

Experimental study on slender buckling-restrained knee braces with round steel bar cores

This study aimed to investigate a novel slender buckling-restrained knee brace damper (BRKB) for welded and weld-free steel framing systems. The proposed BRKB adopts steel bar cores connected by a central coupler and restrained by tube buckling restrainers with a cover tube supporter. The advantages of the proposed damper include easy assembly compared to conventional buckling restrained braces, and high architectural flexibility for the retrofitting of large-span weld-free or welded steel moment-resisting systems. Specifically, by increasing the number of contraction allowances, undesirable failure mechanisms that are global instability and local buckling of the restrainer ends can be effectively suppressed because the more uniform plastic deformation of the core bar can be achieved longitudinally. In this study, displacement-controlled compression and cyclic loading tests were carried out to investigate the deformation capacities of the proposed BRKBs. Structural performance metrics associated with both loading tests, such as strength capacities, strains at the cover tubes and buckling restrainers, and hysteretic behaviors of the proposed damper under cyclic loads, were measured and discussed. Test results revealed that the geometrical characteristics of the cover tubes and adopted contraction allowances at the dampers play essential roles in their load-bearing capacities.

余交换Hopf代数上Yang-Baxter方程的解

研究了Hopf brace的一些性质,并利用Rota-Baxter算子和Hopf brace探索了在余交换Hopf代数上Yang-Baxter方程的解,并给出了解在余交换Hopf代数k[G]上的具体形式.

A spatiotemporal deep learning method for excavation-induced wall deflections

Data-driven approaches such as neural networks are increasingly used for deep excavations due to the growing amount of available monitoring data in practical projects.However,most neural network models only use the data from a single monitoring point and neglect the spatial relationships between multiple monitoring points.Besides,most models lack flexibility in providing predictions for multiple days after monitoring activity.This study proposes a sequence-to-sequence(seq2seq)two-dimensional(2D)convolutional long short-term memory neural network(S2SCL2D)for predicting the spatiotemporal wall deflections induced by deep excavations.The model utilizes the data from all monitoring points on the entire wall and extracts spatiotemporal features from data by combining the 2D convolutional layers and long short-term memory(LSTM)layers.The S2SCL2D model achieves a long-term prediction of wall deflections through a recursive seq2seq structure.The excavation depth,which has a significant impact on wall deflections,is also considered using a feature fusion method.An excavation project in Hangzhou,China,is used to illustrate the proposed model.The results demonstrate that the S2SCL2D model has superior prediction accuracy and robustness than that of the LSTM and S2SCL1D(one-dimensional)models.The prediction model demonstrates a strong generalizability when applied to an adjacent excavation.Based on the long-term prediction results,practitioners can plan and allocate resources in advance to address the potential engineering issues.

Deterministic and probabilistic analysis of great-depth braced excavations:A 32 m excavation case study in Paris

The Fort d’Issy-Vanves-Clamart(FIVC)braced excavation in France is analyzed to provide insights into the geotechnical serviceability assessment of excavations at great depth within deterministic and probabilistic frameworks.The FIVC excavation is excavated at 32 m below the ground surface in Parisian sedimentary basin and a plane-strain finite element analysis is implemented to examine the wall deflections and ground surface settlements.A stochastic finite element method based on the polynomial chaos Kriging metamodel(MSFEM)is then proposed for the probabilistic analyses.Comparisons with field measurements and former studies are carried out.Several academic cases are then conducted to investigate the great-depth excavation stability regarding the maximum horizontal wall deflection and maximum ground surface settlement.The results indicate that the proposed MSFEM is effective for probabilistic analyses and can provide useful insights for the excavation design and construction.A sensitivity analysis for seven considered random parameters is then implemented.The soil friction angle at the excavation bottom layer is the most significant one for design.The soil-wall interaction effects on the excavation stability are also given.

Clinical effect of operative vs nonoperative treatment on humeral shaft fractures:Systematic review and meta-analysis of clinical trials

BACKGROUND Whether operation is superior to non-operation for humeral shaft fracture remains debatable.We hypothesized that operation could decrease the nonunion and reintervention rates and increase the functional outcomes.AIM To compare the clinical efficacy between operative and nonoperative approaches for humeral shaft fractures.METHODS We searched the PubMed,Web of Science,ScienceDirect,and Cochrane databases from 1990 to December 2023 for clinical trials and cohort studies comparing the effects of operative and conservative methods on humeral shaft fractures.Two investigators independently extracted data from the eligible studies,and the other two assessed the methodological quality of each study.The quality of the included studies was assessed using the Cochrane risk bias or Newcastle-Ottawa Scale.The nonunion,reintervention and the overall complications and functional scores were pooled and analyzed using Review Manager software(version 5.3).RESULTS A total of four randomized control trials and 13 cohort studies were included,with 1285 and 1346 patients in the operative and nonoperative groups,respectively.Patients in the operative group were treated with a plate or nail,whereas those in the conservative group were managed with splint or functional bracing.Four studies were assessed as having a high risk of bias,and the other 13 were of a low risk of bias according to the Newcastle-Ottawa Scale or Cochrane risk bias tool.The operative group had a significantly decreased rate of nonunion[odds ratio(OR)0.30;95%CI:0.23 to 0.40,reintervention(OR:0.33;95%CI:0.24 to 0.47),and overall complications(OR:0.62;95%CI:0.49 to 0.78)].The pooled effect of the Disabilities of Arm,Shoulder,and Hand score showed a significant difference at 3[mean difference(MD)-8.26;95%CI:-13.60 to-2.92],6(MD:-6.72;95%CI:-11.34 to-2.10),and 12 months(MD:-2.55;95%CI:-4.36 to-0.74).The pooled effect of Visual Analog Scale scores and the Constant-Murley score did not significantly differ between the two groups.CONCLUSION This systematic review and meta-analysis revealed a trend of rapid functional recovery and decreased rates of nonunion and reintervention after operation for humeral shaft fracture compared to conservative treatment.

Finite Element Analysis of Tubular KK Joint under Compressive Loading

KK tubular joints are used to build jacket-type offshore structures. These joints are mostly made up of structural steel. These joints can withstand yield, buckling, and lateral loads depending on the structure’s design and environment. In this study, the Finite Element Model of the KK-type tubular joint has been created, and analysis has been performed under static loading using the Static Structural analysis system of ANSYS 19.2 commercial software and structural mechanics module of COMSOL Multiphysics. The KK tubular model is analyzed under compressive load conditions, and the resulting stress, strain, and deformation values are tabulated in both graphical and tabular form. This study includes a comparison of the outcomes from both commercial software. The results highlight that maximum stress, strain, and deformation values decrease as joint thickness increases. This study holds significant relevance in advancing the understanding of tubular KK joints and their response to compressive loading. The insights derived from the analysis have the potential to contribute to the development of more robust and reliable tubular KK joints in various engineering and structural applications. .

Triply Factorised Groups and the Structure of Skew Left Braces

The algebraic structure of skew left brace has proved to be useful as a source of settheoretic solutions of theYang-Baxter equation.We study in this paper the connections between left and right π-nilpotency and the structure of finite skew left braces.We also study factorisations of skew left braces and their impact on the skew left brace structure.As a consequence of our study,we define a Fitting-like ideal of a left brace.Our approach depends strongly on a description of a skew left brace in terms of a triply factorised group obtained from the action of the multiplicative group of the skew left brace on its additive group.

Skew Braces of Size p^(2)q I:Abelian Type

This is the first part of a series of two articles.In this paper we enumerate and classify the left braces of size p^(2)q,where p and q are distinct prime numbers,by the classification of regular subgroups of the holomorph of the abelian groups of the same order.We also provide the formulas that define the constructed braces.