Analysis on column-bracing forces considering random initial imperfections

A large number of column-bracing systems were modeled and analyzed by second-order analysis using finite element program ANSYS,in which the random combination of the initial imperfections between columns and horizontal braces was well considered by Monte Carlo Method.According to the analysis results,four kinds of instability modes of column-bracing systems were found,the probability density function of the mid-height horizontal bracing forces was established based on probability statistics,and the design bracing forces were also obtained.The results indicated that the above design bracing forces are smaller than that proposed by the "Code for design of steel structures"(GB50017-2003) when the top axial compressions on the braced columns are equal,and much smaller than the latter when the top axial compressions on the braced columns are unequal.The results also indicated that the random combination of the initial imperfections between columns and horizontal braces leads to the randomness of the mid-height horizontal bracing forces in compression or in tension,so that the design bracing forces can be reduced.

Effects of bottom bracings on torsional dynamic characteristics of horizontally curved twin I-girder bridges with different curvatures

Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads. This study investigates the effects of bottom bracings on the torsional dynamic characteristics of CTIGBs. Five types of bottom bracings are designed to investigate their effects on the dynamic characteristics of CTIGBs with different curvatures under free and forced vibrations. To perform numerical investigations, three-dimensional (3-D) finite element (FE) bridge and vehicle models are established using commercial ANSYS code, and then a vehicle-bridge interaction analysis approach is proposed. Road roughness profiles generated from power spectral density and cross spectral functions are also taken into account in the analyses. The numerical results show that torsional frequencies increase significantly after providing bottom bracings, and the increasing rate depends on the type of bottom bracings and their locations of installation. Bottom bracings can act as load transmitting members from one main girder to the others. Large negative bearing forces that have occurred in bridges with small radii of curvatures can be remarkably reduced by providing bottom bracing systems. It is found that the performances of several bottom bracing systems are effective in improving the torsional dynamic characteristics of the bridges in this study.

Mechanical compression release device in steel bracing system for retrofitting RC frames

The development of an innovative structural system with satisfactory seismic performance of braced systems is an important and challenging area of interest in structural engineering. In this paper, a device that can release the compressive force in the bracing members is developed, and its performance is evaluated. For comparison, four steel braced RC frames were constructed and tested under reverse cyclic loads. Two of them had different amounts of bracing and the other two had the same amount of bracing but incorporated different type of device, called compression release device, which is developed and described in this paper. It can be concluded from the test results that the newly developed device can effectively be used in steel braced systems to prevent buckling failure of the bracing members. Therefore, the device enhances the ductility of brace-framed systems by allowing an adequate capacity for energy dissipation.

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.

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.

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.

Curve evolution during bracing in children with scoliosis secondary to early-onset neurofibromatosis type 1:indicators of rapid curve progression

Background:Scoliosis secondary to neurofibromatosis type 1(NF1)in children aged<10 years is an important etiology of earlyonset scoliosis(EOS).This study was performed to investigate the curve evolution of patients with EOS secondary to NF1 undergoing bracing treatment and to analyze high-risk indicators of rapid curve progression.Methods:Children with EOS due to NF1 who underwent bracing treatment from 2010 to 2017 were retrospectively reviewed.The angle velocity(AV)at each visit was calculated,and patients with rapid curve progression(AV of>10°/year)were identified.The age at modulation and the AV before and after modulation were obtained.Patients with(n=18)and without rapid curve progression(n=10)were statistically compared.Results:Twenty-eight patients with a mean age of 6.5±1.9 years at the initial visit were reviewed.The mean Cobb angle of the main curve was 41.7°±2.4°at the initial visit and increased to 67.1°±8.6°during a mean follow-up of 44.1±8.5 months.The overall AV was 6.6°±2.4°/year for all patients.At the last follow-up,all patients presented curve progression of>5°,and 20(71%)patients had progressed by>20°.Rapid curve progression was observed in 18(64%)patients and was associated with younger age at the initial visit and a higher incidence of modulation change during follow-up(t=2.868,P=0.008 and<0.001,respectively).The mean AV was 4.4°±1.2°/year before modulation and 11.8°±2.7°/year after modulation(t=11.477,P<0.010).Conclusions:Curve progression of>10°/year is associated with younger age at the initial visit,and modulation change indicated the occurrence of the rapid curve progression phase.

Evaluation of the Surgical Treatment of Patella Fractures in 17 Cases in the Orthopedic-Traumatology Department of the University Hospital Center of Donka, Republic of Guinea

Objectives: To determine the epidemiological, therapeutic and evolutionary aspects. Methodology: This was a retrospective study, from January 1, 2016 to December 31, 2018, on the files of patients aged 16 and over, admitted for patella fractures, treated surgically and followed up in our service. Results: The study involved 17 patients including 15 men (88.24%) and 02 women (11.76%) with an average age of 36.65 years. Workers were the most represented (29.42%);AVP were the leading cause of these fractures (52.94%). The fractures were open in 70.58% of cases. Associated lesions were dominated by femur fractures in 29.42%. Duparc type II was the most encountered bone lesion with 47.06% of cases. All our patients benefited from regional anesthesia. Bracing was the most used surgical treatment in 58.83%;the anterior approach was performed in all our patients. Four (04) cases of knee stiffness, two (02) postoperative infections and skin necrosis complicated the short and medium term consequences. After a two-year follow-up, radiologically one case of pseudarthrosis and one case of patellofemoral osteoarthritis were noted. According to the Bosman score, we found 17.65% excellent, 47.06% good and 35.29% poor functional results. Conclusion: Patella fractures are relatively rare. Treatment is primarily surgical for transverse and/or displaced fractures;Bracing is the osteosynthesis technique of choice. However, knee stiffness, pseudarthrosis and patellofemoral osteoarthritis are not uncommon.

Inelastic displacement ratio of low-to mid-rise BRBFs designed under variable levels of seismicity

Buckling-restrained braces(BRBs)have shown their capability to provide building structures with stiffness,strength,and ductility.Estimating the seismic drifts of buckling-restrained braced frames(BRBFs)is an important design step to control structural and non-structural damage.In current practice of seismic design,the estimation of seismic drifts of BRBFs is performed by using empirical calculations that are independent upon either the type of the structural system or the design level of seismicity.In these empirical calculations,the seismic drifts are estimated by amplifying the reduced elastic drifts obtained under design lateral loading with a displacement amplification factor(DAF).The value of DAF is considered equal to the product of the response modification factor R and the inelastic displacement ratioρ.The goal of the current research is to assess the value ofρfor low-to mid-rise BRBFs designed under low and high levels of seismicity.This goal has been achieved by conducting a series of elastic and inelastic time-history analyses pertaining to an ensemble of earthquake records on 3-,6-and 9-story BRBFs.The results indicate that theρ-ratio increases with an increase in design seismic intensity and an increase in experienced inelasticity.The range ofρfor low seismicity designs ranges from 0.63 to 0.9,while for high seismicity designs this range stretches from 0.83 to 1.29.It has been found that the consideration of a generalρ-ratio of 1.0 is a reasonable estimation for the design of the BRBFs considered in this study.

一类brace中的thin边

证明若一个brace含有一个四圈C_(4),且该四圈中包含两个相邻的三度点,则该brace至少有一条thin边在该C_(4)中.

Internal brace与带线锚钉通过改良Broström术治疗慢性踝关节不稳的疗效对比

目的比较internal brace(IB)与带线锚钉通过改良Broström术治疗慢性踝关节不稳的临床疗效。方法回顾性分析2019年5月至2022年2月在桂林市人民医院本院关节骨科行手术治疗的42例慢性踝关节外侧不稳患者资料,根据距腓前韧带修补所用材料的不同将患者分为IB组(19例)和带线锚钉组(23例)。比较两组患者一般资料、手术时间、并发症发生率、术后完全负重行走时间、术后恢复跑步的时间、美国足踝外科协会(American Orthopedic Foot and Ankle Society,AOFAS)踝-后足功能评分、视觉模拟评分法(visual analog scale,VAS)评分。结果所有患者术后均获得随访,随访时间12~18个月,平均(13.8±5.3)个月。两组患者基线资料差异无统计学意义(P>0.05);两组各有1例术口拆线后再出现渗液,换药后愈合;两组各有2例术口区域感觉障碍,除IB组有1例术后半年仍未完全恢复外,其余3例术后2~3个月恢复;IB组患者术后6周随访时AOFAS评分优于带线锚钉组,差异有统计学意义(t=2.239,P=0.025),但术后6周时VAS评分比较差异无统计学意义(t=0.308,P=0.760);末次随访时AOFAS评分和VAS评分比较,两组之间差异无统计学意义(t=0.045,P=0.965;t=0.203,P=0.840);IB组术后完全负重行走时间、术后恢复跑步的时间显著早于带线锚钉组,差异有统计学意义(t=26.566,P<0.01;t=4.838,P<0.01)。结论IB与带线锚钉通过改良Broström术开放治疗慢性踝关节不稳的临床疗效满意,且使用IB在早期康复和重返运动方面优于带线锚钉。

Shaking table experimental study of recycled concrete frame-shear wall structures

In this study, four 1/5 scaled shaking table tests were conducted to investigate the seismic performance of recycled concrete frame-shear wall structures with different recycled aggregates replacement rates and concealed bracing detail. The four tested structures included one normal concrete model, one recycled coarse aggregate concrete model, and two recycled coarse and fi ne aggregate concrete models with or without concealed bracings inside the shear walls. The dynamic characteristics, dynamic response and failure mode of each model were compared and analyzed. Finite element models were also developed and nonlinear time-history response analysis was conducted. The test and analysis results show that the seismic performance of the recycled coarse aggregate concrete frame-shear wall structure is slightly worse than the normal concrete structure. The seismic resistance capacity of the recycled concrete frame-shear wall structure can be greatly improved by setting up concealed bracings inside the walls. With appropriate design, the recycled coarse aggregate concrete frame-shear wall structure and recycled concrete structure with concealed bracings inside the walls can be applied in buildings.

Effectiveness of two conventional methods for seismic retrofit of steel and RC moment resisting frames based on damage control criteria

This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation methods, concentric chevron bracing（CCB） and cylindrical friction damper（CFD） were selected. The performance assessment procedure of the frames is divided into two distinct phases. First, the limit state probabilities of the structures before and after rehabilitation are investigated. In the second phase, the seismic risk of structures in terms of life safety and financial losses（decision variables） using the recently published FEMA P58 methodology is evaluated. The results show that the proposed retrofitting methods improve the serviceability and life safety performance levels of steel and RC structures at different rates when subjected to earthquake loads. Moreover, these procedures reveal that financial losses are greatly decreased, and were more tangible by the application of CFD rather than using CCB. Although using both retrofitting methods reduced damage state probabilities, incorporation of a site-specific seismic hazard curve to evaluate mean annual occurrence frequency at the collapse prevention limit state caused unexpected results to be obtained. Contrary to CFD, the collapse probability of the structures retrofitted with CCB increased when compared with the primary structures.

A hybrid artificial bee colony algorithm and support vector machine for predicting blast-induced ground vibration

Because nearby construction has harmful effects,precisely predicting blast-induced ground vibration is critical.In this paper,a hybrid artificial bee colony(ABC)and support vector machine(SVM)model was proposed for predicting the value of peak particle velocity(PPV),which is used to describe blast-induced ground vibration.To construct the model,5 potentially relevant factors,including controllable and uncontrollable parameters,were considered as input parameters,and PPV was set as the output parameter.Forty-five samples were recorded from the Hongling lead-zinc mine.An ABC-SVM model was developed and trained on 35 samples via 5-fold cross-validation(CV).A testing set(10 samples)was used to evaluate the prediction performance of the ABC-SVM model.SVM and four empirical models(United States Bureau of Mines(USBM),Amraseys-Hendron(A-H),Langefors-Kihstrom(L-K),and Central Mining Research Institute(CMRI))also were introduced for comparison.Next,the performances of the models were analyzed by using 3 statistical parameters:the correlation coefficient(R2),root-mean-square error(RMSE),and variance accounted for(VAF).ABC-SVM had the highest R2 and VAF values followed by the SVM,A-H,USBM,CMRI,and L-K methods.The results demonstrated that ABC-SVM outperformed SVM and the empirical predictors for predicting PPV.Moreover,the best results from the R2,RMSE,and VAF indices were 0.9628,0.2737,and 96.05%for the ABC-SVM model.The sensitivities of the parameters also were investigated,and the height difference between the blast point and the monitoring station was found to be the parameter that had the most influence on PPV.

Seismic risk assessment for developing countries: Pakistan as a case study

Modern Earthquake Risk Assessment（ERA） methods usually require seismo-tectonic information for Probabilistic Seismic Hazard Assessment（PSHA） that may not be readily available in developing countries. To bypass this drawback, this paper presents a practical event-based PSHA method that uses instrumental seismicity, available historical seismicity, as well as limited information on geology and tectonic setting. Historical seismicity is integrated with instrumental seismicity to determine the long-term hazard. The tectonic setting is included by assigning seismic source zones associated with known major faults. Monte Carlo simulations are used to generate earthquake catalogues with randomized key hazard parameters. A case study region in Pakistan is selected to demonstrate the effectiveness of the method. The results indicate that the proposed method produces seismic hazard maps consistent with previous studies, thus being suitable for generating such maps in regions where limited data are available. The PSHA procedure is developed as an integral part of an ERA framework named EQRAM. The framework is also used to determine seismic risk in terms of annual losses for the study region.

A study on the seismic behavior of a retrofitted building based on nonlinear static and dynamic analyses

This study describes the seismic performance of an existing five storey reinforced concrete building which represents the typical properties of low-rise non-ductile buildings in Turkey. The effectiveness of shear walls and the steel bracings in retrofitting the building was examined through nonlinear static and dynamic analyses. By using the nonlinear static analysis, retrofitted buildings seismic performances under lateral seismic load were compared with each other. Moreover, the performance points and response levels of the existing and retrofitting cases were determined by way of the capacity-spectrum method described in ATC-40 (1996). For the nonlinear dynamic analysis the records were selected to represent wide ranges of duration and frequency content. Considering the change in the stiffness and the energy dissipation capacities, the performance of the existing and retrofitted buildings were evaluated in terms of story drifts and damage states. It was found that each earthquake record exhibited its own peculiarities, dictated by frequency content, duration, sequence of peaks and their amplitude. The seismic performance of retrofitted buildings resulted in lower displacements and higher energy dissipation capacity depending mainly on the properties of the ground motions and the retrofitting strategies. Moreover, severe structural damage (irreparable or collapse) was observed for the existing building. However, buildings with retrofit alternatives exhibited lower damage levels changing from no damage to irreparable damage states.

Location Results for Brace Spacing in Gap Tubular “K” Joints Using FEM

The 8-node iso-parametric thin shell element was employed in the study of stress concentrations in the welded tubular “K” joint. Element equilibrium equations were derived using isoparametric formulation based on thin shell theory. After assembly, the resulting system equations were solved using existing fortran programs. Numerical experiments were conducted to isolate and locate ideal gap (positions) for the two braces of the “K” joint. The nominal stresses were calculated from which stress concentration factors were obtained. The resulting stress concentration factors were presented both as tables and as figures. A good agreement between our solutions and those for model joints in the literature is good and acceptable. It was found that the wider apart the brace spacing is, the weaker the strength of the joint. It was also found that the best location for the braces occurs when the stress level changes sign either from positive to negative or vice versa at a critical sampling point.

Behavior of ductile steel X-braced RC frames in seismic zones

A satisfactory ductile performance of moment-resisting reinforced concrete concentric braced frame structures (RC-MRCBFs) is not warranted by only following the provisions proposed in Mexico’s Federal District Code (MFDC-04). The nonlinear behavior of low to medium rise ductile RC-MRCBFs using steel X-bracing susceptible to buckling is evaluated in this study. The height of the studied structures ranges from 4 to 20 stories and they were located for design in the lakebed zone of Mexico City. The design of RC-MRCBFs was carried out considering variable contribution of the two main lines of defense of the dual system (RC columns and steel braces). In order to observe the principal elements responsible for dissipating the earthquake input energy, yielding mappings for diff erent load-steps were obtained using both nonlinear static and dynamic analyses. Some design parameters currently proposed in MFDC-04 as global ductility capacities, overstrength reduction factors and story drifts corresponding to diff erent limit states were assessed as a function of both the considered shear strength and slenderness ratios for the studied RC-MRCBFs using pushover analyses. Additionally, envelopes of response maxima of dynamic parameters were obtained from the story and global hysteresis curves. Finally, a brief discussion regarding residual drifts, residual drift ratios, mappings of residual deformations in steel braces and residual rotations in RC beams and columns is presented. From the analysis of the obtained results, it is concluded that when a suitable design criterion is considered, good structural behavior of RC-MRCBFs with steel-X bracing can be obtained. It is also observed that the shear strength balance has an impact in the height-wise distribution of residual drifts, and an important “shake-down” eff ect is obtained for all cases. There is a need to improve design parameters currently proposed in MFDC to promote an adequate seismic performance of RC-MRCBFs.

Conceptual study of X-braced frames with different steel grades using cyclic half-scale tests

In this paper, an experimental and analytical study of two half-scale steel X-braced flames with equal nominal shear strength under cyclic loading is described. In these tests, all members except the braces are similar. The braces are made of various steel grades to monitor the effects of seismic excitation. Internal stiffeners are employed to limit the local buckling and increase the fracture life of the steel bracing. A heavy central core is introduced at the intersection of the braces to decrease their effective length. Recent seismic specifications are considered in the design of the X-braced frame members to verify their efficiency. The failure modes of the X-braced frames are also illustrated. It is observed that the energy dissipation capacity, ultimate load capacity and ductility of the system increase considerably by using lower grade steel and proposed detailing. Analytical modeling of the specimens using nonlinear finite element software supports the experimental findings.