梁刚度对现浇混凝土空心楼板受力的影响

在现浇混凝土空心楼板中,梁的竖向变形和刚度对空心楼板的内力存在着较大的影响。文章采用PKPM-SLABCAD复杂楼板有限元软件对竖向荷载作用下,梁-空心楼板相互作用关系进行分析。通过调整梁与空心楼板抗弯刚度比来分析梁刚度对现浇混凝土空心楼板的影响。     

宽扁梁现浇空心楼板竖向受力性能研究

通过对湖南某高层建筑中局部两开间布置带宽扁梁的大跨度现浇空心楼板进行现场水箱加载试验,研究空心楼板在竖向荷载作用下的竖向位移、裂缝开展及分布特征,同时引入空心层分层壳模型对该空心楼板进行了有限元受力性能分析。结果表明,在设计活荷载作用下,带宽扁梁的大跨度现浇空心楼板具有足够的抗弯刚度和抗裂能力,能够满足现行规范正常使用极限状态的要求。但由于宽扁梁与空心楼板刚度比为1.5,宽扁梁对空心楼板无法形成有效嵌固而导致竖向荷载作用下,两开间试验现浇空心楼板的竖向位移曲线、裂缝分布与单块板基本相似。分析结果亦表明,空心层分层壳模型能较好地实现对空心楼板受力性能的模拟,当宽扁梁高与空心楼板厚度比h_b/h_s≥2时,宽扁梁可实现对空心楼板的有效约束,可供实际工程选用。     

现浇混凝土GBF高强薄壁管空心楼板施工

现浇混凝土GBF高强薄壁管空心楼板由暗梁和非抽芯式空心楼板组成,无明梁、无柱帽,暗梁与空心楼板同厚,重量比实心无梁楼板轻,而承载能力等同于实心无梁楼板,形成大跨度明梁楼盖体系.     

预应力平行圆管混凝土空心板柱结构地震后承载力试验研究

建造了一个4层现浇无粘结预应力混凝土空心板柱结构的1/4比例模型,分别进行地震前第3层楼板弹性范围内的荷载试验和地震后第1层楼板极限荷载试验,通过测量楼板挠度、钢筋应力及空心楼板的裂纹发展情况,探求预应力混凝土空心板柱结构地震的损伤破坏,楼板的承载能力的变化情况。试验结果表明,在相同荷载作用下,楼板跨中、平行布管方向预应力暗梁和垂直布管方向预应力暗梁跨中地震后挠度均大于地震前。空心楼板的整体性较好,强烈地震对楼板的刚度响应较小,楼面承载力试验过程仍可划分为三个阶段:弹性阶段,开裂扩展阶段和破坏阶段。地震对垂直布管方向预应力暗梁刚度影响大于平行布管方向预应力暗梁,垂直布管方向预应力暗梁跨中挠度地震后比地震前增大程度明显大于平行布管预应力暗梁。基于前述试验结果,并考虑空心楼板的裂纹发展情况,建立了空心楼板极限荷载状态下的塑性铰线分析模型,计算空心楼板的极限荷载略小于试验结果,计算结果与试验数据吻合较好。     

现浇混凝土无梁空心楼板的设计与应用研究

文章介绍现浇混凝土无梁空心楼板的设计原理、施工方法及质量控制措施,比较无梁空心楼板与普通钢筋混凝土有梁板结构之间存在的优点和不足,从而论述这种结构型式选用的原则。     

楼梯配筋中易犯的三种错误

<正>施工中,给楼梯下料配筋,要注意不要犯以下3种错误。错误1:板式楼梯斜板配筋。在实际工程中,有时出现板式楼梯斜板在支座处负筋数量不足、跨中分布筋数量不足的情况。因考虑板式楼梯斜板刚度小,若两端与平台梁、平台板及楼盖梁、楼板整体相连,支座的约束作用较为显著,因而斜板跨中和支座弯矩近似取M=±al2/10,支座负筋数量应与跨中相同。同时要注意在每个踏步下应至少配置一根直径为8mm或10mm     

现浇钢筋混凝土空心楼板施工技术

结合工程实例,阐述了现浇无梁空心楼板工程施工的工艺原理、施工技术要点以及质量保证措施,实践证明,与有梁预制空心楼板相比,其综合效益明显,以期推广现浇钢筋混凝土空心楼板的应用。     

钢筋套筒挤压搭接连接预制空心楼板-叠合梁节点试验

为研究受拉钢筋套筒挤压搭接连接的预制空心楼板-叠合梁连接节点在竖向荷载作用下的受力性能,进行了2个筒芯内模布设方向不同的预制空心楼板-叠合梁连接节点和1个现浇空心楼板-叠合梁连接节点的静力试验。结果表明:3个试件的裂缝分布相同、破坏形态相同,均为空心楼板受弯破坏;试件的试验承载力与规范计算承载力的比值均大于1.05,可采用规范正截面受弯承载力公式计算预制空心楼板的受弯承载力;试件的名义屈服荷载、峰值荷载、峰值点割线刚度基本相同;预制空心楼板受拉钢筋套筒挤压搭接接头可有效传递钢筋拉力。     

人致激励下装配式竹集成材空心楼板舒适度试验研究

进行了人致激励下装配式竹集成材空心楼板的舒适度试验,选用了自振频率与峰值加速度为舒适度的评价指标。利用了抬脚跟激励方式来获得楼板在不同工况条件下的自振频率,分析了人行荷载作用下楼板动力响应,可以发现:空载时楼板自振频率都超过规定限值(3Hz)的6倍,负载时楼板的自振频率也都超过10 Hz;所有工况人行激励试验的楼板峰值加速度都小于0.015g,跨度小、两端铰接的楼板动力响应加速度值最大,跨度大、两端固接时板的峰值加速度最小。结果表明装配式竹集成材空心楼板满足舒适度要求。     

浅谈现浇混凝土空心楼板

现浇混凝土空心楼板在工程项目中应用越来越多,与普通现浇梁板结构相比具有自身优势。本文对现浇混凝土空心楼板在设计及施工中应注意的问题做了具体介绍。     

Theoretical investigations on load‐bearing capacity of RC flat‐plate framed structures subject to middle column loss

This paper presents theoretical studies on load‐bearing capacity of reinforced concrete flat‐plate framed structures. The existing methods for determining load‐bearing capacity of simply supported slabs are first reviewed, and their limitations are presented. An energy‐based refined method is then proposed to enhance the accuracy of the existing methods by considering the contributions to internal energy dissipation due to the extension of reinforcing bars along yield lines, the additional resultant bending moment from membrane forces, and the sectional bending moment along yield lines of slabs. The refined method for simply supported slabs is extended for fixed supported slabs, and thus, the load‐bearing capacity of reinforced concrete flat‐plate structures subject to a middle column loss is analytically determined. The performance of the proposed method is validated against test results and also verified against finite element analyses. Parametric studies are conducted to investigate the effect of reinforcement ratio, slab thickness and aspect ratio on the stiffness, and yield‐line resistance of structures. It is found that for the fixed supported slabs, it is reasonable to assume negative yield lines along the slab edges to consider the effect of obvious concrete crushing along the edge. Square slabs have higher ultimate loads than rectangular slabs, due to a longer horizontal yield line in the middle in the rectangular slab, which has detrimental effect on the sectional ultimate bending moment. The numerical results show that the reinforcement ratio has little effect on the initial bending stiffness and yield‐line resistance of slabs for a given slab thickness and aspect ratio. The initial stiffness and yield‐line resistance increase as the slab thickness increases. For the same reinforcement ratio and slab thickness, a larger aspect ratio leads to a lower initial bending stiffness, yield‐line resistance, and stiffness in tensile membrane action stage, due to a longer yield line along which tensile membrane forces have a detrimental effect on the sectional bending moment.     

预应力混凝土叠合板与底板(实心、空心)受弯承载力相关关系试验研究

通过理论与试验研究，分析了预应力混凝土底板(实心、空心)与叠合板开裂弯矩相关性、抗弯极限承载力相关性，提出了二者相关关系模式与相应的计算方法，为叠合板与底板结构性能检验提供了新的检验方法与计算手段，弥补了叠合板与底板结构性能现有检验方法的不足，可供有关规范及通用标准图集编制和生产、检验部门参考试用。     

Moment coefficients for design of waffle slabs with and without openings

The direct design method recommended by ACI is commonly used for the design of flat slabs. Since the flexural stiffness of the waffle slab varies along the span, it is expected that the distribution of moments is different from that of flat slabs. Current design procedures do not provide recommendations specific of waffle slabs. Designers smear the contribution of the ribs and use the design guidelines for flat slabs to design ribbed slabs. In addition, the effect of openings on the response of waffle slabs is not fully explored. Therefore, modified moment coefficients are needed for waffle slabs. In this paper, numerical simulations using ANSYS are used to study the response of waffle slabs with and without openings. The main objectives of this paper are: (1) to obtain the design coefficients for the column and the field strips of the internal panel of a waffle slab and (2) to study the effect of openings and stiffening ribs on the design coefficients. Ninety Linear and non-linear analysis models using ANSYS were performed in the study to evaluate the response of various waffle slabs under uniform loading. The main parameters evaluated are the column size, the solid portion size, the opening size and its location, and the effect of stiffener ribs around the opening. The non-linear finite element model was verified using existing experimental results for two waffle slabs. The moment coefficients developed in this paper were used to modify the existing ACI flat-slab coefficients to be used for waffle slabs.     

Analysis of lateral load transfer by internal slab-column joints

The results of an analytical study examining the behavior and load transfer mechanism of 16 interior flat slab-column joint models, transferring lateral load, are presented. Predictions of the connection response were calculated using a professional finite element computer program, utilizing three-dimensional, elasto-plastic, concrete elements.

Currently, various analytical methods are suggested for calculating the load transfer. The assume that the slab sections carry the external unbalanced moment by developing a bending moment on the front and back faces, and a torsional moment on the side faces. Several studies have tried to determine the relative contribution of the bending and torsional moments. Slots or cutting through the slab, made along the respective column faces, were introduced in an attempt to isolate the components that resist the external moment.

According to the present analysis, the various types of connections have a minor effect on the response. They display very similar deformations and stress distributions in the slab, except for very local stress concentrations, almost ignoring the slots and cuttings. As a result of this analysis, the attempts to isolate appear to be unsuitable since the slab's bending and torsional mechanisms are highly coupled.     

SMW围护结构内插型钢弯矩估算方法研究

SMW是一种采用就地搅拌水泥土体然后内插型钢形成的连续柔性挡土结构,适用于深基坑,有良好的应用前景.为保证基坑安全,需对其内插型钢的弯矩承载力发挥情况做到心中有数,但就目前的工程现状来看,直接得到内插型钢的真实弯矩很困难.作者根据深基坑工程中常规监测得到的SMW围护结构的测斜曲线,提出了一种根据变形曲线反算弯矩的简便方法,能够直接为广大工程人员掌握.这种估算方法的应用,可以节约深基坑工程中的监测费用,及时了解地下围护结构中型钢承载力发挥情况,提前采取措施避免由于设计不合理引起的工程事故.     

无柱帽空心无梁楼盖设计中若干问题的探讨

指出了在空心无梁楼盖中采用薄壁管作为填充构件的不足之处，分析了无梁楼盖与双向板在传力机制与受力变形上的差异，阐述了南京东苑大厦中采用薄壁盒作为填充构件的无柱帽空心无梁楼盖的结构设计与施工要点。     

Fire performance assessment of HPLWC hollow core slabs through full-scale furnace testing

High-Performance Light-Weight Concrete (HPLWC) is used for many structural applications when superior strength and low self-weight of the structural components are required. Among these applications there are thin floor structures, like hollow core slabs, that require characteristics of lightness, relatively high resistance and superior durability. Although the fire performance of normal strength concrete hollow core slabs has been extensively studied, the behavior of HPLWC hollow core slabs has not been suitably investigated.The paper reports the results of two full-scale furnace tests on HPLWC hollow core slabs. Each of them involved one panel with an applied load and one without load. The evolution of temperature inside the slabs was measured along with the load bearing capacity under fire conditions. During the first test severe spalling occurred in the loaded slab while during the second one, performed on slabs cured for some months under dry conditions, spalling did not occur. Finite elements simulations were also carried out in order to support the interpretation of the experimental results. Experimental and numerical investigations gave insight into the fire performance of HPLWC hollow core slabs and highlighted the influence of dry curing conditions in reducing the spalling and increasing the fire resistance.     

Interaction of twin tunnels and shallow foundation at Zand underpass, Shiraz metro, Iran

Tunnel construction in urban areas may inevitably require crossing close to adjacent structures. In this paper, the driving of Shiraz metro twin tunnels beneath Zand underpass of a major municipal artery built 15 years ago has been analyzed. The earth pressure balance (EPB) operation parameters consisting of face pressure, grout pressure and thrust force, which are effective on the ground movement and tunnels-underpass interaction, were investigated. For precise analysis, the effects of twin tunnels construction on modification of normal forces and bending moments of the underpass structural members and first tunnel lining were also studied. The results showed that, face pressure as compared to grout pressure and thrust force had a more significant impact on the underpass settlement. The rate of displacement differences because of increasing those EPB operation parameters at tunnel crown was greater than the surface and piles toe of the underpass. The changes in normal forces of the underpass were greater than bending moments, which could be related to high bending moment of the underpass members. The normal forces showed remarkable variations in the upper concrete plate of the underpass. The effects of second tunnel construction on the first one, regarding to the changes in normal forces, bending moments and displacements showed less than 10% increment.     

压型钢板-混凝土双向组合板实用计算方法

根据压型钢板-混凝土组合板的受力特点,讨论单、双向组合板的判断标准;提出双向组合板实用计算中考虑泊松比影响的跨中弯矩修正方法;对双向组合板荷载传递与各向同性的普通混凝土楼板的区别进行比较,提出方便实用的荷载传递计算方法。     

现浇钢筋混凝土暗扁梁空心楼盖的施工质量控制

简述了CBM空心内模管及现浇钢筋混凝土暗扁梁空心楼盖结构的特点,并结合工程实例,介绍了现浇钢筋混凝土暗扁梁空心楼盖的施工技术及CBM管的安装和固定措施,提出了施工过程中要注意的施工要点及问题.