Strength of bolted moment connections in ferrocement construction

In continuation of an experimental investigation reported earlier by the authors on bolted moment joints in ferrocement construction, this study regards (1) further testing of ten such joints to broaden the range of the principal parameters – thickness of the connected ribs and location of bolts and (2) simple analytical modeling for design. Test results, as presented and discussed in this paper, indicate that the mode of failure of a joint depends on whether the applied moment is in the opening or closing mode. Under the closing mode, failure always occurs by shear punching of the bearing plates through the connected ribs. In contrast, failure in the opening mode occurs by bending failure of either the connected or the longitudinal rib. Based on observed failure modes, expressions have been derived for predicting the strength of such a joint. A comparison of theoretical predictions with present test results and those reported earlier shows good agreement.     

Repair and strengthening of reinforced concrete square columns using ferrocement jackets

A series of 10 one-third scale square reinforced concrete column specimens were cast; preloaded under axial compression up to various fractions (0%, 60%, 80%, and 100%) of its ultimate load; repaired using ferrocement jackets containing two layers of Welded Wire Mesh (WWM) encapsulated in high strength mortar; and then retested to failure. The overall response of the specimens was investigated in terms of load carrying capacity, axial displacement, axial stress and strain, lateral displacement, and ductility. The test results indicated that jacketing reinforced concrete square columns with this form of ferrocement provided about 33% and 26% increases in axial load capacity and axial stiffness, respectively, compared to the control columns. The test results also indicated that repairing similar reinforced concrete columns (after preloading them to failure) with the same ferrocement jacket almost restored their original load capacity and stiffness. Furthermore, the repaired columns failed in a ductile manner compared to the brittle failure exhibited by the control columns.     

Behaviour of ferrocement confined reinforced concrete (FCRC) under axial compression

An experimental investigation on the behaviour of ferrocement confined reinforced concrete (FCRC) under axial compression, by varying the specific surface factor (S_f) which controls the behaviour of ferrocement, is presented. A total of 270 prisms of size 150×150×300 mm were tested. The results indicated that additional confinement in the form of ferrocement shell improved the ultimate strength, strain at ultimate strength and the ductility of concrete. The improvement is in proportion to the S_f of the ferrocement shell for a given confinement index (C_i) of the lateral reinforcement.     

Development of pseudo-ductile permanent formwork for durable concrete structures

The present investigation focuses on a new approach for the construction of durable concrete structures. Using Pseudo-ductile Cementitious Composites (PDCC) of relatively low water/binder ratio, permanent formworks are first fabricated. Normal concrete is then cast to make structural components. With low permeability and high crack resistance, the permanent formwork acts as effective surface cover to prevent the corrosion of steel reinforcements. The formwork can be made with PDCC alone, or with the incorporation of Glass Fiber Reinforced Plastics (GFRP) rods. In some structural components, the GFRP reinforcements will be sufficient to provide the necessary load-carrying capacity. When higher loads are to be carried, steel reinforcements can be added to produce a component with very high durability (due to the thick cover to steel) as well as ductile behavior. This paper focuses on mechanical aspects of this construction concept. The development of PDCC for formwork fabrication is first described. The bond between PDCC and concrete, in relation to various surface treatment methods, will be investigated with beam specimens. Test results on concrete beams made with GFRP reinforced PDCC formwork are then presented and compared to theoretical predictions. A design example is performed to demonstrate the use of GFRP/PDCC permanent formwork for constructing the deck of a footbridge. The results of this investigation show promise of the technology for practical applications.     

Testing structural concrete beam elements

A method for testing structural concrete beam and column elements subjected to axial load, bending moment and shear is described. The information presented includes: the test set-up, with particular emphasis on how the loads are applied using a combination of hydraulic actuators and rigid links connected to a yoke at each end of the specimen; the specimen boundary conditions which were designed to reduce the shear transferred by strut action; as well as highlights from the first 17 tests which involved monotonic shear, reverse cyclic shear and reverse cyclic axial load on beam elements up to 350 mm×700 mm in cross-section.     

Use of recycled concrete aggregate in high-strength concrete

The results of a test programme to study the use of recycled concrete aggregate (RCA) in high-strength, 50 N/mm² or greater, concrete are described. The effects of coarse RCA content on the ceiling strength, bulk engineering and durability properties of such concretes have been established. The results showed that up to 30% coarse RCA had no effect on concrete strength, but therafter there was a gradual reduction as the RCA content increased. A method of accommodating the effects of high RCA content, involving simple adjustment to water/cement ratio of the mix is given. It is shown that high-strength RCA concrete will have equivalent engineering and durability performance to concrete made with natural aggregates, for corresponding 28-day design strengths. The practical implications of the study for concrete construction are discussed.

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Résumé Sont décrits ici les résultats d’une série d’essais destinés à étudier l’utilisation de granulats provenant du recyclage d’éléments en béton (RCA) dans des bétons de haute résistance (50 MPa et plus). Les effets de la teneur en gros granulats recyclés sur la résistance des plafonds et des batiments, ainsi que les propriétés de tels bétons ont été établis. Les résultats ont montré qu’une teneur allant jusqu’à 30% en gros granulats recyclés n’a pas d’effet sur la résistance du béton, mais qu’au dessus de 30%, la résistance diminue progressivement à mesure que la teneur en gros granulats recyclés augmente. Une méthode visant à accommoder les effets dus à une forte proportion de RCA, nécessitant un simple ajustement du rapport eau/ciment dans le mélange, est proposée. Il est prouvé que le béton RCA de haute résistance aura des qualités de résistance et de durabilité équivalentes à celles de bétons constitués de granulats naturels, pour les résistances mécaniques à 28 jours prévues. Les implications pratiques de l’étude sur la réalisation d’ouvrages en béton sont présentées.

     

钢筋钢纤维混凝土梁柱节点模型化方法研究

为研究钢筋钢纤维混凝土梁柱节点抗震性能数值模拟方法,基于OpenSEES有限元平台中的梁柱节点单元(beam-column joint element, BCJE)模型,通过修正模型中剪切块和钢筋滑移弹簧的参数修正方法,提出适用于钢筋钢纤维混凝土梁柱节点的数值模型,并基于6个梁柱节点的拟静力试验结果进行模型验证分析,数值模拟结果与试验结果吻合较好,提出的数值模型能够较精确地反映节点滞回行为。在此基础上,分析了轴压比、钢纤维体积率和配箍量对梁柱节点抗震性能的影响规律,建立了节点受剪承载力的计算公式。结果表明:掺入钢纤维和增加配箍可明显改善梁柱节点的抗震性能,钢纤维体积率从0.5%增加到2.0%,极限荷载提高了18%;箍筋从1Φ8增加到3Φ8时,极限荷载提高了19.7%。     

Test unit for analyzing deformed specimens of beam construction models

A functional scheme, procedure, and technical capabilities of a test unit for simulating and analyzing the spectral and strain characteristics with vibration of elements of beam structures are described. A scheme and calibration procedure are provided for optical measurement of unit movements. An example is given of using the test unit for spectral analysis of the vibrations of a triangular model beam structure with a defect in the form of a crack of different depth. __________ Translated from Izmeritel’naya Tekhnika, No. 3. pp. 31–34, March, 2008.     

Ultimate moment capacity of ferrocement reinforced with weldmesh

An improved qualitative mechanical model which is thought to reflect more realistically the behaviour of ferrocement in flexure is presented. In light of this model, three types of existing typical quantitative models of ultimate moment capacity based on yield strength of wire, nonlinear stress-strain function for cold-worked wire and ultimate wire strength have been evaluated. For singly weldmesh reinforced ferrocement the model based on ultimate wire strength is found to be simpler, more reliable and more economical than the other two types of models. For uniformly reinforced ferrocement a new model based on yield strength proposed by the authors appears to be more reliable and economical, and simpler than other models based on yield wire strength. A simpler and more economical model based on ultimate wire strength for uniformly weldmesh reinforced ferrocement is also put forward by the authors. This model shows a closer agreement with test results than the existing models based on yield wire strength or nonlinear stress-strain function for cold-worked wire.     

Evaluation of Portland limestone cements for use in concrete construction

The paper describes a study carried out to examine the performance of concrete produced using combinations of Portland cement (PC) and limestone (LS), covering compositions for Portland limestone cement (PLC) conforming to BS EN 197-1: 2000, and up to 45% LS. In particular, key engineering (mechanical) and durability properties of concrete were studied. The results indicate only minor differences in performance between PC and 15% PLC concretes of the same cement content and water/cement (w/c) ratio (cement = Portland cement + addition). However, there was an adverse effect with increasing LS content beyond 15% of the cement content for many properties. It is shown that for 35 N/mm² cube strength concrete the adjustment to w/c ratio to match the compressive strength of PC concrete was in the region of 0.08 for each 10% LS added (water curing at 20°C) above this level. Studies of permeation and concrete durability performance, including, initial surface absorption, carbonation resistance, chloride diffusion, freeze/thaw scaling and abrasion resistance, indicate that in general the test concretes followed single relationships with strength for most properties. Consideration is given to the practical implications of the main outcomes of the study.     

不同位移边界条件下钢筋混凝土深梁拓扑优化

为了探讨位移边界条件对钢筋混凝土深梁拓扑优化的影响,同时为深梁设计提供有效的力学理论依据,以ANSYS有限元分析软件为平台,利用其参数化设计语言的二次开发功能,并借助具有直观高效拓扑寻优能力的渐进演化类算法,分别对4根支座约束条件不同的双侧开洞深梁、4根开洞情形不同的两端固定铰支深梁以及3根支座约束与开洞情形均有一定差别的连续深梁进行拓扑优化,并对不同拓扑解进行对比分析。结果表明：集中力作用下深梁的拓扑解均近似为杆系结构,提高支座约束程度可以使传力路径增加,传力方式更直接;当深梁因工程原因或功能需求而不得不设置洞口时,洞口位置离原传力路径越远则越有利于结构内部的传力;连续深梁与单跨深梁的拓扑解的主要差别体现在中支座处的梁顶拉杆上,这些拉杆能够提高结构的整体刚度。因此,在工程设计中,针对不同位移边界条件下的钢筋混凝土深梁,可以根据它们拓扑解的差异以及造成这些差异的力学机理,采取不同的设计方案,包括支座约束、开洞情形以及配筋方式等的选取。研究结果可为深梁这类复杂受力构件的设计提供力学理论依据。     

Reliability of ferrocement slabs under cyclic thermal-shock loading

The reliability of ferrocement slabs subjected to cyclic thermal-shock loading induced by raindrops during service is investigated. The data are obtained experimentally by subjecting specimens to heating and wetting cycles and monitoring the residual first-crack strength at different periods. The imposed thermal-shock loads simulate actual service conditions and are estimated by monitoring the temperature of typical roofing slabs just before the commencement of rain over a period of time. The mean deterioration in strength obtained after correcting for curing effects due to ageing and temperature, as well as the uncertainty present, are used to assess the reliability of slabs having residual first-crack strengths above some prescribed values at different periods. The results indicate that ferrocement slabs posses good flexural resistance with respect to the cyclic loadings studied and are suitable for use as roofing elements.     

Use of laminated mechanical joints with metal and concrete plates for precast concrete columns

This study investigated the structural behavior of a mechanical joint with laminated concrete and metal plates for moment connections which can be used for the rapid erection of reinforced concrete precast columns. A concrete filler plate was placed between the metal column plates to transfer loads and protect nuts threaded with rebars. Nonlinear numerical finite element analyses considering concrete damaged plasticity was also performed to evaluate the load–displacement relationship, plate deformation of the joints with concrete filler plates, and rates of strain increase of the structural components. The influence of the column and concrete filler plates on the rate of strain increase of the structural components attached to the column plates was explored to determine how concrete, rebars, and steel sections, were activated relative to the stiffness of the metal plates. The strain values of structural elements that were attached to plates with sufficient stiffness values were found to be higher than those of the structural elements that were attached to plates with smaller stiffness values. These strains were evident in the nonlinear finite element analyses and experimental investigations. It can be inferred that laminated mechanical plates consisting of metal and concrete plates can be implemented and used to replace conventional precast connections.     

Bond-slip behavior of self-compacting concrete and vibrated concrete using pull-out and beam tests

This paper analyzes the bond behavior of an innovative construction material, self-compacting concrete (SCC), in comparison to vibrated concrete (VC), using pull-out and beam tests according to the Rilem procedures. The main analyzed parameters were the concrete compressive strength, the steel bar diameter, the concrete type and the test adequacy to provide a value for bond strength. Also, a comparison between Code provisions and empirical equations was done. According to the results, SCC and VC specimens presented similar behavior. The equations results showed a satisfactory approach compared to the experimental ones, but as expected Code provisions were very conservative. Based on the obtained results, it could be concluded that the same parameters adopted for VC can be extended for SCC.     

Experimental and numerical analysis of large ferrocement water tanks

In the current work the ferrocement construction technique is revisited with the purpose of applying the material in civil engineering structures, particularly in large water tanks for water treatment stations. Although it is not a new technology, ferrocement continues to be an attractive alternative. The plastic potential, the unsophisticated construction techniques and the low cost justify its use, especially suitable for developing countries. However, modelling studies of this material are rare in the literature; this is what justifies the studies currently being conducted to improve current practices of design, as well as to further advance the understanding of the material. This work describes experimental and numerical tests for large ferrocement tanks, part of the water treatment facility in Divinópolis, Brazil. Different finite element models have been used in the analyses in order to evaluate the effect of some adopted simplifications. Some comparisons of the investigated approaches with the experimental data are also included, as well as remarks on the use of different constitutive models, homogenisation techniques and accuracy of the modelling data.     

Effects of water on permanent deformation potential of asphalt concrete mixtures

This paper presents the results of a primary study on the effects of water on permanent deformation potential of asphalt concrete mixtures by using Asphalt Pavement Analyzer (APA). The same gradation was applied for all mixes. The samples were preconditioned using four different procedures: soaked, saturated, saturated with freeze-thaw conditioning cycle, and preheated. Among the saturated samples and the saturated with freeze-thaw cycle samples, the samples were conditioned to 25%, 50% and 75% degrees of saturation respectively. The freeze-thaw cycles were designed as 1, 4 and 7 cycles. The rut test was performed with APA under wet and dry conditions. All samples saturated with freeze-thaw cycle were tested in wet rut. The results indicate that water influences the rut depths. The depths of wet rut are greater than those of dry rut in most of preconditioning states. Saturation with freeze-thaw cycle, which is normally considered a harsher preconditioning, does not result in larger wet rut depths in this study. At the same freeze-thaw cycle, the wet rut depths of samples decrease with increasing the saturation. At the same saturation, the wet rut depths of samples saturated only are usually greater than those saturated with freeze-thaw cycle.     

大面积混凝土施工质量控制

工业厂房建筑,往往涉及到大面积的钢筋混凝土地面板。在大面积混凝土结构施工中,除应满足混凝土等级、几何尺寸外,表而平整密实和防止混凝土裂缝是施工中必须要严加控制的两个方面,因为这两方面也是在大面积混凝土施工过程中最易出现质量问题的方面。所以在大丽积混凝土施工过程中,结构裂缝和平整度控制是做好质量控制最为重要的控制内容。本文通过天津东疆保税港区物流加1区二期标准仓库、厂房项目（一标段）工程零层板混凝土浇筑经历,叙述施工过程中采取的预控及过程控制措施,防止了裂缝及不平整现象的发生。     

针对大体积混凝土施工裂缝应采取的措施

从大体积混凝土施工的特点出发,结合实例,分析温度裂缝产生原因和防治措施。