一种新型装配式钢骨混凝土节点的抗震性能研究

为了避免装配式钢骨混凝土节点核心区的破坏,提出一种可实现损伤部位转移的新型节点形式.以框架边节点为研究对象,建立7组节点数值模型,开展低周反复荷载试验.从混凝土等效塑性应变、钢筋骨架Mises应力、节点滞回曲线和骨架曲线等方面计算分析,探究混凝土强度等级、柱轴压比、焊接位置、梁柱强度比等参数的影响.结果表明:装配式节点可将损伤位置从核心区转移到梁端;增加混凝土强度等级,可提高节点承载能力,但节点耗能能力和延性会下降;调整柱轴压比,可减小等效塑性应变,但对钢筋骨架应力、耗能能力、承载能力等影响极小;增加焊接位置至柱边距离,可使节点损伤部位外移,屈服后刚度和承载力有所提高,但耗能能力有所下降;增加梁柱强度比能够改善节点的耗能能力和承载力,但当强度比超过0.6时,梁端与节点核心区应力差变小.     

一种新型装配式钢骨混凝土节点的抗震性能研究

为了避免装配式钢骨混凝土节点核心区的破坏,提出一种可实现损伤部位转移的新型节点形式.以框架边节点为研究对象,建立7组节点数值模型,开展低周反复荷载试验.从混凝土等效塑性应变、钢筋骨架Mises应力、节点滞回曲线和骨架曲线等方面计算分析,探究混凝土强度等级、柱轴压比、焊接位置、梁柱强度比等参数的影响.结果表明:装配式节点可将损伤位置从核心区转移到梁端;增加混凝土强度等级,可提高节点承载能力,但节点耗能能力和延性会下降;调整柱轴压比,可减小等效塑性应变,但对钢筋骨架应力、耗能能力、承载能力等影响极小;增加焊接位置至柱边距离,可使节点损伤部位外移,屈服后刚度和承载力有所提高,但耗能能力有所下降;增加梁柱强度比能够改善节点的耗能能力和承载力,但当强度比超过0.6时,梁端与节点核心区应力差变小.     

钢骨混凝土偏压长柱受力性能试验研究

为了研究细长钢骨混凝土柱在偏心荷载作用下的性能,文章进行了10根钢骨混凝土偏心受压长柱的试验,主要变化参数为混凝土强度、试件长细比和荷载作用偏心距。主要研究了柱子的长细比、荷载作用的偏心距及混凝土强度对柱子承载力的影响。     

硫酸盐侵蚀作用下纤维锂渣混凝土裂缝的分形特征

为探究新型混凝土受硫酸盐侵蚀后的力学性能,采用质量分数为5%的硫酸盐溶液全浸泡加速侵蚀法,对11组聚丙烯纤维混凝土（PC）试块、11组聚丙烯纤维锂渣混凝土（PLiC）试块、8根PC大偏心受压柱和8根PLiC大偏心受压柱进行侵蚀试验,得到了不同侵蚀时间下混凝土的力学性能。基于分形理论分析了试块及构件破坏时表面裂缝分布的分形特征,详细讨论了试块及构件表面裂缝分形维数与其侵蚀时间、抗压强度、极限承载力之间的关系。研究表明,PC和PLiC立方体抗压强度随侵蚀天数先增加后降低,在120 d达到最大;试块及构件破坏时表面裂缝分布具有分形特征,试块表面裂缝分形维数随侵蚀天数的增加呈现先增加后减少再增加的规律,随试块抗压强度的提高而减少;PC及PLiC混凝土大偏心柱极限承载力随侵蚀天数的增加先增加后减少,锂渣的掺入可以提高聚丙烯纤维混凝土柱的抗硫酸盐侵蚀能力,构件破坏时表面裂缝分形维数随硫酸盐侵蚀天数呈现震荡上升的趋势;因此混凝土表面裂缝的分形特征可作为判定构件损伤程度的指标之一,可为今后对在役混凝土结构承载力和寿命预测提供参考。      

金川矿区深部巷道支护效果评价及参数优化研究

巷道支护问题一直是矿业工程中的难题,特别是在深部软岩巷道中,能否提供持久、有效的支护直接影响着矿山的安全生产和可持续发展。“双层网锚喷+U型钢拱架”联合支护是目前金川矿区在深部巷道支护中较常用的支护方案,为了解该方案的支护效果,在二矿区814 m分斜坡道上设立试验段,采用现场监测与数值模拟计算相结合的方法,对该试验段巷道的支护效果进行评价,并针对支护的薄弱部分提出改进措施。研究结果表明：（1）在当前支护条件下,巷道顶板和两帮围岩得到了较好的控制,但底鼓问题严重,最大位移可达110 cm;（2）针对当前支护方案的薄弱环节,提出增加锚杆长度、提高锚杆强度和增加底板支护等补强措施;（3）设计了一组参数优化方案,并对其支护效果进行了数值模拟分析,认为该优化支护方案能够有效地控制巷道围岩变形,并弥补原支护方案的缺陷。     

考虑楼板效应的外环板式梁柱节点抗弯承载力

楼板的存在对梁柱节点的局部受力影响显著, 在梁柱节点设计中, 若仅仅把楼板与钢梁的组合效应作为安全储备, 可能会产生结构由"强柱弱梁"转变成"强梁弱柱"的颠覆性结果, 因此忽略混凝土楼板对节点承载力及刚度的影响是造成破坏的重要原因.基于已完成的带楼板的T型梁柱节点低周往复荷载试验, 建立了非线性有限元分析模型.为了更加全面地了解钢梁-楼板组合节点的工作机制, 进一步补充完善试验研究的不足, 模型考虑了楼板与钢梁之间的栓钉连接以及材料非线性等因素, 模型的计算结果与试验结果具有高吻合度.在此基础上, 通过有限元参数分析, 详细分析了构件尺寸效应、轴压比、楼板厚度、楼板强度和柱宽厚比共五个参数对考虑楼板影响的外环板式梁柱节点抗震性能的影响.结果表明尺寸效应、轴压比对梁端抗弯承载力及刚度的影响小到可以忽略, 楼板厚度、楼板强度和柱宽厚比对梁端抗弯承载力有显著影响.结合理论分析进一步提出了考虑楼板影响的外环板式梁柱节点梁端抗弯承载力计算公式, 通过对比公式计算结果与试验、有限元分析结果可得, 该计算公式可较好的计算带楼板外环板式梁柱节点梁端抗弯承载力.      

轻钢 - 轻质混凝土结构在看台台阶中的应用

轻钢主要指轻型冷弯薄壁型钢、轻型焊接和高频焊接型钢、薄壁钢板、薄壁钢管、轻型热轧型钢及以上各型材的组合,其具有强度高和自重轻的特点,能充分发挥其材料特性并带来施工便利的建筑材料。轻钢 -轻质混凝土结构具有结构自重轻、抗震性能好、施工速度快、劳动强度低等优点,目前行业内常见的轻钢墙体有空心墙体和实心墙体两种,空心墙体常采用 OSB 板 ( 欧松板）或水泥板加保温隔音棉,实心墙体多采用现浇轻质混凝土。实心墙体为代表的轻钢 - 轻质混凝土结构,为了便于后期自密实轻质混凝土灌浆施工,在轻钢结构龙骨架安装完成后,需要在墙体两面挂上免拆模板钢丝网,将事先按设计密度搅拌好的轻质混凝土进行墙体浇筑。银川市三沙源防沙治沙学院体育看台工程中,台阶就采用轻钢 - 轻质混凝土结构,与传统的混凝土结构相比,降低了看台板的厚度和配筋率,由于自重减小而基础尺寸也相应减小,项目实施后效果良好。     

开挖卸荷扰动下的深部巷道支护及其效果评价

为了解决某金矿深部巷道存在的围岩灾变损伤严重、支护结构濒临失效的问题,开展了有关深部巷道开挖卸荷和采动影响耦合作用下的开挖损伤研究,并针对性地提出围岩变形控制方案。运用FLAC^3D软件从应力集中—迁移演化、位移场和塑性区分布3个方面对该支护方案的支护效果进行深入探讨,并结合现场工程试验监测所获得的实时原位数据进行分析对比。研究结果表明：深部破碎化巷道在开挖扰动下塑性区扩展趋势明显,两帮肩部及侧墙底角处应力集中程度较高,底板所受破裂损伤压力最大,高应力向巷道深部迁移,最终巷道开挖影响区停留在半径的2~4倍。同时,验证了针对这种工程环境所施加的喷—锚—网联合支护替代传统的U型钢架、锚杆支护做补强支护这一围岩控制方案能够更好地发挥破碎化围岩的自承载能力,有效抵御巷道的变形破坏,具有良好的支护效果,能够为类似工程环境的矿山深部巷道围岩变形控制和支护设计提供合理化建议。     

应力与硫酸铵耦合作用对混凝土强度的影响

为研究应力腐蚀下混凝土强度变化规律及特点,将混凝土试块分别浸泡在质量分数为0、1.0％、2.5％和5.0％硫酸铵溶液中,同时施加轴压应力,将压应力水平持续保持为极限抗压强度的0、20％和40％.结果表明:硫酸铵溶液对混凝土存在明显的腐蚀作用,混凝土极限抗压强度随硫酸铵浓度升高而不断下降;压应力的存在可以抑制硫酸铵溶液对混凝土的腐蚀作用,且随着应力水平的提高,抑制效果逐渐增强.基于试验数据建立了混凝土蚀强模型,误差范围满足要求且具有一定普适性,可为实际工程提供参考.     

应力与硫酸铵耦合作用对混凝土强度的影响

为研究应力腐蚀下混凝土强度变化规律及特点,将混凝土试块分别浸泡在质量分数为0、1.0％、2.5％和5.0％硫酸铵溶液中,同时施加轴压应力,将压应力水平持续保持为极限抗压强度的0、20％和40％.结果表明:硫酸铵溶液对混凝土存在明显的腐蚀作用,混凝土极限抗压强度随硫酸铵浓度升高而不断下降;压应力的存在可以抑制硫酸铵溶液对混凝土的腐蚀作用,且随着应力水平的提高,抑制效果逐渐增强.基于试验数据建立了混凝土蚀强模型,误差范围满足要求且具有一定普适性,可为实际工程提供参考.     

Strengthening of Interior Slab–Column Connections Using a Combination of FRP Sheets and Steel Bolts

The results of an experimental investigation undertaken to evaluate a new technique for strengthening interior slab–column connection in combined flexural and shear modes are presented. The technique consists of using a combination of shear bolts inserted into holes and prestressed against the concrete surface for improving the punching shear capacity, and external [fiber-reinforced polymer (FRP)] reinforcement bonded to the tension face of the slabs in two perpendicular directions for increasing the flexural strength of the slabs. Square slab specimens of 670×670?mm dimensions were tested and the main test variables included the ratio of steel reinforcement (1.0 and 1.5%), span–depth ratio or thickness (55 and 75?mm) of the slabs, area, and configuration of steel bolts, and area of FRP reinforcement. It was found that the use of shear bolts alone improves the punching shear strength and increases the ductility of failure by changing the failure mode from punching to flexural. However, the use of a combination of shear bolts and a moderate amount of FRP reinforcement increased the flexural strength and resulted in a substantial improvement of the punching shear capacity of the slabs. The corresponding increases attained levels between 34 and 77%. A design approach is presented for evaluating the ultimate capacity of the slab–column connections when strengthened using the proposed strengthening technique. Strength results predicted by the proposed approach were in good agreement with the experimental results.     

双钢板混凝土组合剪力墙轴压承载力研究

首先对双钢板混凝土组合剪力墙中的钢板进行了屈曲理论分析,对核心受约束混凝土进行了受力分析.以北京中国尊核心筒结构底部剪力墙为原型,进行了1/4缩尺模型的双钢板混凝土组合剪力墙试件和内置钢板混凝土组合剪力墙的轴压性能试验,对比分析其荷载-位移曲线、轴压承载力等.考虑到钢板屈曲对钢板轴压承载力的影响以及受约束混凝土轴心抗压强度的提高,提出了双钢板混凝土组合剪力墙轴压承载力的计算公式,与应用其他计算方法计算得到的试验试件的轴压承载力相比,本文提出的计算公式的计算结果与试验结果吻合度最高.结合其他文献中双钢板混凝土组合剪力墙轴压性能试验的相关数据进行验证,表明利用本论文提出的计算公式得到的轴压承载力计算值与试验结果吻合较好.      

Behavior of Gravity Load-Designed Rectangular Concrete Columns Confined with Fiber Reinforced Polymer Sheets

This study concentrates on analytical evaluation of the effect of external confinement using fiber reinforced polymers (FRP) sheets on the response of concrete rectangular columns designed for gravity load only and having spliced longitudinal reinforcement at the column base. A general analytical scheme for evaluating the strength capacity and ductility of the columns under combined flexural–axial loads was developed. The analysis takes into account the bond strength degradation of the spliced reinforcement with increase in lateral load by incorporating a generalized bond stress–slip law, and considers the effect of FRP confinement on the stress–strain response of concrete material. Particular emphasis is placed in the analysis on the slip response of the spliced bars and the consequent fixed end rotation that develops at the column base. Results predicted by the analysis showed very good agreement with limited experimental data. A parametric evaluation was carried out to evaluate the effect of different design and strength parameters on the column response under lateral load. Without confinement, the columns suffered premature bond failure and, consequently, low flexural strength capacity. Confining the concrete in the columns end zone at the splice location with FRP sheets enhanced the bond strength capacity of the spliced reinforcement, increased the steel stress that can be mobilized before bond failure occurs, and consequently improved the flexural strength capacity and ductility of the columns. A general design equation, expressed as a function of the main parameters that influence the bond strength capacity between spliced steel bars and FRP confined concrete, is proposed to calculate the area of FRP sheets needed for strengthening of the subject columns.     

Axial Load Capacity of Concrete-Filled FRP Tube Columns: Experimental versus Theoretical Predictions

This paper presents the experimental and theoretical results of small and medium-scale concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) columns. A total of 23 CFFT specimens were tested under axial compression load. Five different types of new FRP tubes were used as stay-in-place formwork for the columns. The effects of the following parameters were examined: the FRP-confinement ratio, the unconfined concrete compressive strength, the presence of longitudinal steel reinforcement, and the height-to-diameter ratio. Comparisons between the experimental test results and the theoretical prediction values by the three North American codes and design guidelines (ACI 440.2R-08, CSA-S6-06, and CSA-S806-02) are performed in terms of confined concrete strength and ultimate load carrying capacity. The results of this investigation indicate that the design equations of the ACI 440.2R-08, CAN/CSA-S6-06, and CAN/CSA-S806-02 overestimate the factored axial load capacity of the short CFFT columns as compared to the yield and crack load levels. Also, the CAN/CSA-S6-06 and CAN/CSA-S806-02 confinement models showed conservative predictions, while the ACI 440.2R-08 was slightly less conservative. A new confinement model is proposed for the confined concrete compressive strength of the CFFT cylinders. Also, the design equations are modified to accurately predict the ultimate and yield load capacities of internally reinforced and unreinforced short CFFT columns. Two new factors are introduced in the modified equations, (kcc) accounts for the in-place-strength of CFFT columns to CFFT cylinder strength, and (kcr) accounts for the initiation of the steel yielding and concrete cracking for the FRP-confined columns.     

Analytical Model for FRP Confinement of Concrete Columns with and without Internal Steel Reinforcement

The paper aims to contribute to a better understanding of the behavior of reinforced concrete columns confined with fiber-reinforced polymer (FRP) sheets. In particular, some new insights on interaction mechanisms between internal steel reinforcement and external FRP strengthening and their influence on efficiency of FRP confinement technique are given. In this context a procedure to generate the complete stress-strain response including new analytical proposals for (1) effective confinement pressure at failure; (2) peak stress; (3) ultimate stress; (4) ultimate axial strain; and (5) axial strain corresponding to peak stress for FRP confined elements with circular and rectangular cross sections, with and without internal steel reinforcement, is presented. Interaction mechanisms between internal steel reinforcement and external FRP strengthening, shown by some experimental results obtained at the University of Padova with accurate measurements, are taken into account in the analytical model. Four experimental databases regarding FRP confined concrete columns, with circular and rectangular cross section with and without steel reinforcement, are gathered for the assessment of some of the confinement models shown in literature and the new proposed model. The proposed model shows a good performance and analytical stress-strain curves approximate some available test results quite well.     

Assessing the Efficiency of CFRP Discrete Confinement Systems for Concrete Cylinders

Concrete columns requiring strengthening intervention always contain a certain percentage of steel hoops. Applying strips of wet layup carbon fiber-reinforced polymer (CFRP) sheets inbetween the existent steel hoops might, therefore, be an appropriate confinement technique with both technical and economic advantages, when full wrapping of a concrete column is taken as a basis of comparison. To assess the effectiveness of this discrete confinement strategy, circular cross-sectional concrete elements confined by distinct arrangements of strips of CFRP sheet are submitted to a direct compression load up to the failure point. The influence of the width of the strip, distance between strips, number of CFRP layers per strip, CFRP stiffness, and concrete strength class on the increase of the load carrying capacity and ductility of concrete columns, is evaluated. An analytical model is developed to predict the compressive stress-strain relationship of concrete columns confined by discrete and continuous CFRP arrangements. The main results of the experimental program are presented and analyzed and used to assess the model performance.     

Behavior of Beams Strengthened with Novel Self-Anchored Near-Surface-Mounted CFRP Bars

A commonly observed failure mode in laboratory tests involving surface bonded fiber-reinforced polymer (FRP) laminates or near-surface-mounted (NSM) bars is premature delamination, that is, the separation of the FRP from the substrate well before the FRP reaches its ultimate strain capacity. To delay the onset of delamination and to ensure that the NSM FRP reinforcement continues to contribute to member strength after partial delamination, a new self-anchored carbon fiber-reinforced polymer (CFRP) bar was developed and tested for this investigation. This bar is made with a series of monolithic spikes that can be anchored deep inside the concrete. In addition to cutting grooves into the concrete cover for the placement of the primary reinforcing bar, holes are drilled deep into the concrete to insert the spikes. To test the performance of this bar, six large, simply supported, reinforced, concrete beams were retrofitted with NSM bars and tested in four-point bending. Two beams were strengthened with NSM bars without anchors or spikes but were otherwise similar to the self-anchored bar and served as control specimens (Series?B1). Two beams were strengthened in flexure with the new self-anchored NSM bars (Series?B2), and the remaining two beams (Series?B3) were strengthened in flexure and shear by using the self-anchored NSM bars as partial shear reinforcement. The effect of the proposed strengthening system on the beams’ strength, failure mode, deformability, and ductility are discussed on the basis of the experimental results. The anchors delayed delamination and enabled the NSM bar to experience at least a 77% higher strain at failure than the companion bar without anchors. The anchors also increased beam displacement ductility and energy ductility at a 20% strength degradation by at least 34% and 42%, respectively.     

Shear Strengthening of Reinforced Concrete Beams Using Carbon-Fiber-Reinforced Polymer Laminates

Shear failure is catastrophic and occurs usually without advance warning; thus it is desirable that the beam fails in flexure rather than in shear. Many existing reinforced concrete (RC) members are found to be deficient in shear strength and need to be repaired. Externally bonded reinforcement such as carbon-fiber-reinforced polymer (CFRP) provides an excellent solution in these situations. To investigate the shear behavior of RC beams with externally bonded CFRP shear reinforcement, 11 RC beams without steel shear reinforcement were cast at the concrete laboratory of the New Jersey Institute of Technology. After the beams were kept in the curing room for 28?days, carbon-fiber strips and fabrics made by Sika Corp. were applied on both sides of the beams at various orientations with respect to the axis of the beam. All beams were tested on a 979?kN (220?kips) MTS testing machine. Results of the test demonstrate the feasibility of using an externally applied, epoxy-bonded CFRP system to restore or increase the shear capacity of RC beams. The CFRP system can significantly increase the serviceability, ductility, and ultimate shear strength of a concrete beam; thus, restoring beam shear strength by using CFRP is a highly effective technique. An analysis and design method for shear strengthening of externally bonded CFRP has been proposed.     

CFRP-Based Strengthening Technique to Increase the Flexural and Energy Dissipation Capacities of RC Columns

A strengthening technique, combining carbon fiber-reinforced polymer (CFRP) laminates and strips of wet layup CFRP sheet, is used to increase both the flexural and the energy dissipation capacities of reinforced concrete (RC) columns of square cross section of low to moderate concrete strength class, subjected to constant axial compressive load and increasing lateral cyclic loading. The laminates were applied according to the near surface mounted technique to increase the flexural resistance of the columns, while the strips of CFRP sheet were installed according to the externally bonded reinforcement technique to enhance the concrete confinement, particularly in the plastic hinge zone where they also offer resistance to the buckling and debonding of the laminates and longitudinal steel bars. The performance of this strengthening technique is assessed in undamaged RC columns and in columns that were subjected to intense damage. The influence of the concrete strength and percentage of longitudinal steel bars on the strengthening effectiveness is assessed. In the groups of RC columns of 8 MPa concrete compressive strength, this technique provided an increase of about 67% and 46% in terms of column’s load carrying capacity, when applied to undamaged and damaged columns, respectively. In terms of energy dissipation capacity, the increase ranged from 40%–87% in the undamaged columns, while a significant increase of about 39% was only observed in one of the damaged columns. In the column of moderate concrete compressive strength (29 MPa), the technique was even much more effective, since, when compared to the maximum load and energy dissipation capacity of the corresponding strengthened column of 8 MPa of average compressive strength, it provided an increase of 39% and 109%, respectively, showing its appropriateness for RC columns of buildings requiring upgrading against seismic events.     

Fatigue Performance of Concrete Beams Strengthened with CFRP Plates

Recent increases in bridge design loading requirements have highlighted the need for fast, efficient, and durable strengthening methods. External steel plate bonding provides a satisfactory solution, but carbon fiber reinforced plastic (CFRP) offers the added advantages of resistance to corrosion, low weight, and high mechanical strength. This paper examines the fatigue performance of CFRP-strengthened concrete beams as part of a project investigating the use of CFRP as an alternative to steel. Five reinforced concrete beams were tested in fatigue; two control beams and three strengthened with externally bonded CFRP plates. Three loading options were used: (1) apply the same loads to both plated and unplated beams, (2) apply loads to give the same stress range in the rebar in both beams, and (3) apply the same percentage of the ultimate load capacity to each beam. Fatigue fracture of the internal reinforcement steel would appear to be the dominant factor governing failure, and it would appear reasonable to expect the same fatigue life for plated and unplated beams with comparable values of stress range in the steel bar.