钢筋混凝土双向叠合板抗剪强度的极限分析

通过对８块无结合筋双向叠合板的试验研究，本文采用组合周界错动机构，锥面母线为直线与曲线的连线，按塑性极限分析的方法推导了抗剪强度计算公式。该公式与试验结果符合性良好。     

Wheel Load Distribution in Simply Supported Concrete Slab Bridges

This paper presents the results of a parametric study related to the wheel load distribution in one-span, simply supported, multilane, reinforced concrete slab bridges. The finite-element method was used to investigate the effect of span length, slab width with and without shoulders, and wheel load conditions on typical bridges. A total of 112 highway bridge case studies were analyzed. It was assumed that the bridges were stand-alone structures carrying one-way traffic. The finite-element analysis (FEA) results of one-, two-, three-, and four-lane bridges are presented in combination with four typical span lengths. Bridges were loaded with highway design truck HS20 placed at critical locations in the longitudinal direction of each lane. Two possible transverse truck positions were considered: (1) Centered loading condition where design trucks are assumed to be traveling in the center of each lane; and (2) edge loading condition where the design trucks are placed close to one edge of the slab with the absolute minimum spacing between adjacent trucks. FEA results for bridges subjected to edge loading showed that the AASHTO standard specifications procedure overestimates the bending moment by 30% for one lane and a span length less than 7.5 m (25 ft) but agrees with FEA bending moments for longer spans. The AASHTO bending moment gave results similar to those of the FEA when considering two or more lanes and a span length less than 10.5 m (35 ft). However, as the span length increases, AASHTO underestimates the FEA bending moment by 15 to 30%. It was shown that the presence of shoulders on both sides of the bridge increases the load-carrying capacity of the bridge due to the increase in slab width. An extreme loading scenario was created by introducing a disabled truck near the edge in addition to design trucks in other lanes placed as close as possible to the disabled truck. For this extreme loading condition, AASHTO procedure gave similar results to the FEA longitudinal bending moments for spans up to 7.5 m (25 ft) and underestimated the FEA (20 to 40%) for spans between 9 and 16.5 m (30 and 55 ft), regardless of the number of lanes. The new AASHTO load and resistance factor design (LRFD) bridge design specifications overestimate the bending moments for normal traffic on bridges. However, LRFD procedure gives results similar to those of the FEA edge+truck loading condition. Furthermore, the FEA results showed that edge beams must be considered in multilane slab bridges with a span length ranging between 6 and 16.5 m (20 and 55 ft). This paper will assist bridge engineers in performing realistic designs of simply supported, multilane, reinforced concrete slab bridges as well as evaluating the load-carrying capacity of existing highway bridges.     

减少无委托板坯的措施及实践

由于无委托板坯影响企业的资源利用率和合同的完成,使其的管理日益受到重视。宝钢第二炼钢厂无委托板坯源于合同原因、质量原因和规格原因,其中主要是合同和质量的原因。为减少无委托板坯,从无委托板坯产生的源头、操作过程和质量管理等方面采取了措施,使无委托板坯下降50%以上。     

Mechanisms for the intermetallic formation during the Sn-20In-2.8Ag/Ni soldering reactions

The morphology and growth kinetics of intermetallic compounds formed during the interfacial reactions between liquid Sn-20In-2.8Ag solder and Ni substrates are investigated. Energy-dispersive x-ray (EDX) analysis identifies the composition of the interfacial intermetallics as Ni₃(In_0.99In_0.01)₄. The soldering reactions at lower temperatures (225–275°C) result in the predominant formation of a homogeneous intermetallic layer whose growth is diffusion controlled. At higher soldering temperatures (300–350°C), the interfacial intermetallics appear to be long needlelike crystals, and the grooves in between the intermetallics provide fast-diffusion paths for Ni atoms to react with Sn atoms at the intermetallic front, which leads to interface-controlled growth kinetics. The intermetallic needles turned out to be flat slablike after selective etching of the unreacted solder. Kinetics analysis showed that they not only lengthened in the longitudinal direction, but also coarsened transversely by the Ostwald ripening mechanism.     

金刚石组锯绳技术综述

与金刚石砂锯相比,用金刚石组锯绳锯切花岗岩大板具有锯切石材利用率高、对环境友好、板材表面质量好、生产效率高及综合成本低等特点。文章对比了组锯机各主要部件作用及特点,提出了目前国内组锯设备应解决各绳恒张力控制及制造精度等关键问题,组锯绳应解决钢丝绳强度低,串珠配方和结构设计及制造质量稳定等关键问题。     

CFRP 布加固钢筋混凝土双向板抗弯性能分析

选取实际工程中CFRP布加固双向板的实例,利用ANSYS有限元软件建立加固模型,通过逐级递增施加楼面活荷载,对比分析了对比板与加固板的跨中挠度、钢筋应力及承载力,研究了在CFRP布加固方式不同、加固厚度不同及加固量不同时加固板力学性能的规律。结果表明：与对比板相比,CFRP布加固的双向板能有效提高抗弯承载力,减小挠度;贴布面积相同时,分散“＃”字型铺贴加固板效果优于密集“＃”字型和“＋”字型的;适当增加CFRP布粘贴厚度,在原有加固方式基础上增加加固量,均有利于提高板的抗弯承载力;CFRP布宽度增加,有利于提高板的抗弯承载力,但不利于CFRP布强度的发挥。     

反拱水垫塘底板块轴力在上举力作用下的变化规律探讨

为研究反拱水垫塘底板块轴力特征,以溪洛渡高拱坝和反拱水垫塘为参照,在高水头、大流量作用下,以反拱水垫塘在止水破坏、拱圈单底板块、五底板块和九底板块锚固分别失效为代表工况,对拱圈底板块的轴力在上举力作用下的变化规律进行了试验研究。研究表明,拱圈底板块轴力产生和传递的机理是,底板块上举力诱导了底板块位移和锁定,锁定后相邻底板块产生了约束轴力,同时轴力又反过来向相邻底板块传递直至拱端。轴力沿程可分为冲击强振区和上下游强振区。在冲击强振区,底板块瞬时值较大,时均值小,脉动强度最大,拱圈底板能瞬时锁定形成瞬时拱;在上下游强振区,底板块瞬时值和时均值大,而脉动强度较小,拱圈底板块能长时间锁定形成局部拱。在3个强振区,底板块轴力的优势频率在小于0.2 Hz的低频窄带。试验条件下拱圈底板块不发生强度破坏、共振破坏。反拱水垫塘运用时,应控制底板块位移、减少拱圈锁定底板块数,才能使轴力分布在合理范围。     

钢筋混凝土双向板塑性计算表格方法的讨论

本文讨论了“用塑性理论计算钢筋砼双向板的实用表格方法”一文中的一些问题，修正了该文提出的双向板计算方法，补充了一些弯矩系数计算公式及其数值表，供工程设计采用     

板坯自动喷涂技术在热连轧带钢厂的应用

目的降低炉内氧化烧损,提高产品的成材率。方法板坯在上料辊道上及进加热炉前,当检测的板坯温度低于300℃时,利用辊刷及空气吹扫装置清理上下表面后,喷涂一层防高温氧化隔离剂,然后装炉加热,经热连轧成卷。为了减少隔离剂的浪费,提高喷涂效果与设备运行效率,将毛状细钢丝改为钢丝绳,截止阀到喷嘴的距离(需要清洗段)由原约4 m缩短为0.2 m,材质由软塑料管改为内径5 mm的铜管。因上料辊道长度短,超过300℃的热坯必须停留在喷涂罩内,且时间不固定,因此系统设置停留时间≤10 min则继续喷涂,否则,清洗管路,停止喷涂。为了解决停留后需继续喷涂,导致喷涂层厚度不均,最终造成中间坯同块钢出现温度陡降的问题,需要延迟溢流阀门关闭0.5 s,喷涂系统压力维持在0.3 MPa之内。结果成材率可以提高0.3%以上,吨钢涂料消耗控制在0.33 kg以内。结论通过优化喷涂设备结构、材质以及喷涂溢流阀门动作时序,控制系统压力,能实现自动喷涂,获得涂层均匀、节省涂料、提高成材率的效果。