Effect of mix proportion and reinforcement size on the anchorage bond stress of laterized concrete

Lateritic soils, being locally available, have been one of the major building materials in Nigeria, and in most tropical countries in general. This paper reports the results of investigations carried out on the effect of mix proportion and size of plain round steel reinforcement on the anchorage bond stress characteristics of laterized concrete specimens. Laterized concrete is concrete in which some, or all, of the fine aggregate is from lateritic soils.

Sieve analysis of both the lateritic soils and the coarse aggregates used was carried out. Seven different bar sizes (6, 8, 10, 12, 16, 20 and 25 mm) which were cut into pieces 170 mm long to fit into the 150 cube mould were used. Also, three different mix proportions ( and 1:2:4) were used for the study. The results have shown that both the mix proportion and the size of reinforcement have a significant effect on the anchorage bond stress of laterized concrete specimens. The richer, in terms of cement content, the mix proportion, the higher the anchorage bond stress of laterized concrete. Also, the anchorage bond stress between plain round steel reinforcement and laterized concrete increases with increase in the size of reinforcement used.     

PBL加劲型矩形钢管混凝土支管受拉节点有效分布宽度

为研究PBL加劲型矩形钢管混凝土支管受拉节点应力分布规律及其有效分布宽度,采用ABAQUS软件建立42个矩形空钢管、钢管混凝土及PBL加劲型矩形钢管混凝土节点有限元模型并进行位移加载;根据有限元计算结果拟合得到矩形空钢管、钢管混凝土及PBL加劲型矩形钢管混凝土节点的有效分布宽度表达式,将拟合公式计算值与CIDECT规范计算值和有限元计算值进行对比。结果表明:在节点受力全过程中,PBL加劲型矩形钢管混凝土节点相对于矩形空钢管节点和钢管混凝土节点的应力分布不均匀性减小;当加载位移达到3%b₀（b₀为主管宽度）时,PBL加劲型节点的有效分布宽度更大,具有更好的受力性能,支板应力分布效率ξ随主管宽厚比2γ与支主管厚度比τ的增大而减小,其中τ对ξ的影响更大;支板应力分布效率ξ随支主管宽度比β变化较小,且呈抛物线变化;拟合公式计算值与CIDECT规范计算值及有限元计算值吻合良好,验证了公式的正确性     

Effect of temperature on the residual compressive strength of laterized concrete

Tests are reported on 100 mm laterized concrete cubes, containing ordinary portland cement, crushed granite, sharp sand and fine laterite in varying proportions. The percentage of sand by weight of total fine aggregate was varied in steps of 25% up to a maximum of 100% corresponding to normal concrete. The mix proportion was . The test specimens were exposed to varying temperatures ranging from 30°C (i.e. room temperature) to 800°C and allowed to cool for 24 hours before crushing. The results showed that unlike normal concrete the residual compressive strength of laterized concrete increaed, by up to 50% of the nominal strength, with increasing temperature up to 200°C before falling to about 20% of the nominal strength at 800°C. The gain in strength depended on the sand content. The results further showed that within the limits of water/cement ratios normally used in concrete works (i.e. 0.55 to 0.65), the residual strength of laterized concrete was independent of the water/cement ratio. Also, the density of laterized concrete was not significantly affected by changes in temperature but that the tangent modulus of elasticity was reduced from 18 kN/mm² at 30°C to 0.12 kN/mm² at 600°C.     

Influence of method and duration of curing and of mix proportions on strength of concrete containing laterite fine aggregate

In this paper, the influence of six curing methods (water, air, moist soil, jute bag, air/water and water/air) on the compressive strength of concrete cube specimens that contain laterite fine aggregate is investigated. Three different mixes of cement, laterite and gravel were used: ; 1:2:4 and 1:3:6 with water/cement ratios of 0.62, 0.75 and 1.02 by weight respectively. Four curing ages of 7, 14, 21 and 28 days were adopted. The results showed that the strength that a particular mix can attain is affected by the curing method used. The water/air curing technique gave the highest strength values of 28.2 Nmm⁻² for Nmm⁻² and 17.4 Nmm⁻² for 1:2:4 and 1:3:6 mixes respectively, while the air-cured specimens gave the lowest strength values of 17.2 Nmm⁻² for Nmm⁻² and 8.0 Nmm⁻² for 1:2:4 and 1:3:6 mixes. The higher the cement/aggregate ratio the higher the strength. Generally, there was increase in strength with age irrespective of the mix and the curing technique.     

Fire-field modelling on parallel computers

Practical fire-field modelling demands considerable computer resources. This insatiable demand for computer power limited the practice of field modelling to those organisations which had access to expensive computers and applications which could justify the expense. Parallel computing techniques offer the potential of achieving the power required at a fraction of the cost of conventional computer systems. In this paper the development of a fire-field model which has been designed to utilise an arbitrary number of processors operating in parallel cs described. In the implementation discussed here, the processing elements are transputers and the host computer is a 386 based personal computer. However, the adopted approach is not restricted to this particular parallel computing hardware configuration. The capabilities and potentials of the parallel system are demonstrated by performing fire simulations consisting of up to 24 000 computational cells on parallel systems with up to 15 processors. The run time for this simulation has been reduced from over 4 days on a single processor to just over 8 h on the 15 process or system. An interactive graphics system has also been developed which runs in parallel to the main computations.     

FRP筋混凝土梁挠度与裂缝宽度计算模型分析

收集国内外218组纤维增强复合材料(FRP)筋混凝土梁受弯性能试验结果,重点研究了正常使用阶段和极限状态下梁挠度和裂缝宽度的发展规律,基于试验数据修正了FRP筋应变不均匀系数ψ与强度配筋影响系数的关系,建立了该类梁受弯挠度计算模型;深入分析了FRP筋混凝土梁受弯截面内力臂系数η、构件受力特征系数α_cr对构件裂缝宽度计算精度的影响,确定η,α_cr的合理取值,优化计算模型,并与规范GB 50608—2010建议模型计算值进行对比分析。结果表明:根据建立的ψ与强度配筋影响系数关系,选取η=0.88,α_cr=1.5得到的建议模型能够较好预测FRP筋混凝土梁受弯挠度和裂缝宽度,比规范计算结果吻合好,验证了建议模型的准确性和合理性。     

Fire spread in a pallet load of bottles of flammable liquid

This communication reports measurements of the rate and mechanism of fire development in a pallet load of 432 1-litre bottles of xylene, in lots of 12 to a box. The most important result is the specification of the rate of time variation in solvent drainage from the pallet, this can be used—with due account for bunding and drainage arrangements—to determine the rate of heat release and the lateral spread of the burning pool that develops below a burning pallet. It is hoped that these results will aid the design of sprinkler systems for this type of commodity and the assessment of risks in the event of sprinkler failure. These results complement the work of Goodman et al., (J. Fire Sciences, 7 (1989)) who have reported on a series of small-scale experiments to investigate the effects of manipulating packaging variables on the fire performance of plastic bottles containing flammable liquids.     

A comparative study of the potentials of rice husk ash on cohesive and cohesionless soils

In this study, the effects of rice husk ash (RHA) on various geotechnical properties of cohesive (A-7-6 group) and cohesionless (A-1-b group) soils were determined and compared. Atterberg limits, dry density, optimum moisture content, unconfined compressive strength, California bearing ratio, cohesion and angle of internal friction of A-1-b and A-7-6 group soils were studied with different percentages of rice husk ash (0, 4, 8, 12, 16, 20, and 24). Optimum moisture content, compressive strength, California bearing ratio and cohesion of both soils increased with increase in RHA. Maximum dry density decreased with RHA contents. Angle of internal friction of A-7-6 soil increased while that of A-1-b soil decreased with RHA contents. From the point of view of economy and CBR value, A-1-b soil with 16% RHA is recommended for base materials for field trials in the first instance while A-7-6 soil with 17% RHA may be recommended only for sub-base materials.     

洱海泥炭质土动剪切模量和阻尼比试验研究

为探究洱海地域泥炭质土动力学特性,利用GDS动三轴仪对重塑土样进行循环加载试验,得到了一系列围压、固结比、频率控制条件下的泥炭质土动应力-应变关系曲线,分析了不同围压、固结比、频率对土体动剪切模量G_d、动剪切模量比G_d/G_dmax和阻尼比λ的影响规律。结果表明:动剪切模量G_d随剪应变γ_d增大而减小,γ_d较小时,衰减速率较小,随着γ_d继续增大,衰减速率先增大后减小;在同一剪应变下,G_d随围压、固结比增大而增大,G_d对频率变化表现不敏感;采用Hardin-Drnevich双曲线模型(H-D模型)对重塑泥炭质土动应力-应变曲线拟合效果较好,动剪切模量比G_d/G_dmax随剪应变γ_d增大而减小,围压、固结比和频率对G_d/G_dmax的衰减规律无明显的倾向性;阻尼比λ随剪应变γ_d增大而增大,围压对λ变化规律影响较复杂,γ_d较小时,λ随围压增大而减小,γ_d较大时,λ随围压增大而增大;固结比越大,λ越大,频率越大,λ越小,λ对频率变化表现更敏感,体现了循环加载下泥炭质土的速率效应。     

A study of the thermal comfort of primary school children in summer

A study of the thermal comfort and clothing of primary school children aged 7–9 took place during the summers of 1971 and 1972. Of the 641 children who took part, 262 produced records suitable for analysis. The weight of clothing followed the trend of room temperature over several days, but did not respond to diurnal changes of temperature. The subjective warmth followed the variations of room temperature, but was not related to the mean temperatures of the classrooms, which were between 17° and 23°. The children differed significantly among themselves in their subjective response to temperature, but there was no appreciable difference between the responses of the boys and the girls. Thermal comfort distributions are presented and their implications for classroom temperatures are discussed.     

原状与重塑黄土抗拉强度差异性研究

轴向压裂法是一种间接测定土体抗拉强度的试验方法,本文通过该法分析了原状黄土抗拉变形破坏的一般规律以及试样破坏类型。探讨了原状与重塑黄土的劈裂角以及在强度参数比方面(无侧限抗压强度与抗拉强度比以及粘聚力与抗拉强度比)的差异性。结果表明:原状黄土根据抗拉应力-贯入深度曲线走势将变形破坏模式分为3类:弹性变形破坏无残余应力、弹性破坏有残余应力、塑性破坏;原状与重塑黄土在强度参数比方面也存在较大差异。另外,原状黄土劈裂角(α)略小于重塑黄土且均与内摩擦角(φ)呈互补关系;抗拉强度计算公式中的系数K=tan(2α+φ)对于原状黄土建议取值为1.5,对重塑黄土建议取值为2.0。     

Characterization of the California technical bulletin 133 ignition source and a comparable gas burner

The California Bulletin (CB) 133 upholstery ignition source is based on the use of crumpled newsprint. The present work examined the reproducibility of several aspects of this source when placed on an inert chair mock-up. The tendency of this source to heat the side arms of a chair, the area of the seat back subjected to high heat fluxes, the peak flux there and the flux duration all showed substantial variability. For inherently lesser variability a gas burner is preferred. A gas burner, derived from that developed at the British Fire Research Station, was shaped so as to deposit a similar pattern of heat to that of the CB 133 source. The two sources were tested for comparability both on chair mock-ups and on full-scale chairs made from a wide variety of materials. The results indicate that the gas burner, as used here, is a somewhat less severe ignition source than is the CB 133 igniter.     

软土地区盾构隧道弯曲刚度有效率取值研究

修正惯用法以其概念明确、理论成熟和计算便捷的特点在盾构隧道设计中被广泛应用。弯曲刚度有效率η是修正惯用法中的重要参数,其取值对于隧道结构的计算结果具有至关重要的影响。研究基于荷载结构法,利用有限元计算软件ABAQUS建立了匀质圆环模型和梁-弹簧模型,研究了盾构隧道在软土地区通错缝拼装、基床系数和接头相对刚度对弯曲刚度有效率η的影响。通过对数值模拟计算结果进行整理,得到了弯曲刚度有效率η的拟合公式和通错缝拼装弯曲刚度有效率η的转化公式,为确定修正惯用法中的弯曲刚度有效率η提供了计算方法和参考依据。     

Evaluation of deterministic fire models: Part I— Introduction

During 1989 and 1990, a preliminary evaluation of four deterministic fire models was carried out by the University of Edinburgh at the request of the Home Office (London). This paper is the first in a series based on this work and contains material common to the entire study. The models considered were ASET, HAZARD1, FIRST and JASMINE.     

Head losses and friction factors of steady turbulent flows in plastic pipes

Many hydraulic engineering applications, which were once limited to the use of traditional materials, are progressively executed using prefabricated plastic pipes, particularly in the case of larger diameters. There is relatively little information specifically on the laws of flow resistance in plastic tubes, or that has been obtained directly for these materials. In this work, head losses and friction factors were determined experimentally in turbulent steady water flows established in conduits made of different plastics. Several pressure pipes, governed by gravity and forced, with nominal diameters until 110 mm, were used with Reynolds numbers ranging from 4E3 to approximately 6E5. Pairs of values, friction factor vs. Reynolds number, were computed and plotted using logarithmic scales. The layout of the points seems to be generally well represented by the Colebrook-White equation, for each relative roughness. Important absolute roughness variations for the different pipes were found by trend analysis. Blasius and Scimemi empirical formulas for smooth pipes were also plotted and also showed a satisfactory agreement with the experimental data, for Re up to 1E5 and a little less than 1E6, respectively.     

矩形钢管和矩形钢管混凝土T形不等宽受拉节点 轴向刚度

为获得T形节点轴向刚度简化计算公式,根据节点受力特点,提出了适用于矩形钢管节点的平面框架模型和适用于矩形钢管混凝土节点的固端梁模型,并推导得到了2类节点的节点轴向刚度理论公式; 运用有限元方法对节点轴向刚度理论公式中的节点域有效长度l_eff进行参数分析,拟合得到l_eff简化计算公式; 将节点轴向刚度理论公式与试验及有限元结果进行了对比,并分析了主管内填混凝土对节点轴向刚度的影响。结果表明:主管高宽比和主管宽厚比对l_eff的影响较小,不予考虑; l_eff与主管宽度和支管高宽比均呈线性关系,且随之增大而增大; l_eff与支主管宽度比β呈非线性关系,且随之增大而减小; 2类节点的轴向刚度理论公式计算结果与试验结果及有限元结果均吻合较好; 主管内填混凝土可以提高节点轴向刚度,提高系数k_c/h随着主管高宽比的增大而增大,随着β的增大呈现先增大后减小的规律,且当β=0.6～0.7时提高最大。     

Residential cooling loads and the urban heat island—the effects of albedo

The urban heat island has become the target of recent research aiming at improving urban climates and energy efficiency of cities. In the warm, mid- and low-latitude cities, the typical heat island intensity averages up to 3–5°C on a summer day, adding to discomfort and increasing the air-conditioning loads, whereas in some temperate and cold, high-latitude cities a 2°C heat island is considered as a mild asset in winter. Some of these cities have been built to retain the urban heat. The objective of our ongoing research is to identify ways to mitigate summer heat islands in hot climates, for example by increasing the urban albedo, expanding evaporative surfaces and vegetation covers, and increasing urban thermal mass. From the energy consumption point of view, simple techniques such as these can be effective in reducing air-conditioning costs by modifying and improving the urban micro- and meso-climates.

In this work, we have correlated the residential cooling energy and power consumption in Sacramento, California, with the urban heat island intensity. The effects of selected strategies, such as the ones mentioned above, upon changing the urban micro-climate and reducing the heat island induced cooling loads were simulated. The main focus in this paper is placed on albedo. The simulations were performed using the DOE-2.1C building energy analysis program in conjunction with micro-climate and planetary boundary layer models that predict the effects of albedo modifications on ambient conditions and micro-climates. The simulations indicate that there exists significant potential energy and peak power savings by using such simple conservation strategies. Simulations for Sacramento indicate that whitewashing the buildings can result in direct savings of up to 14% and 19% on cooling peak power and electrical cooling energy, respectively. Modifying the overall urban albedo, in addition to whitewashing, can result in total savings of up to 35% and 62% respectively.     

考虑应力路径的软黏土小应变特性试验研究

以苏南地区原状软黏土经K₀固结形成的试样为对象,利用配备了弯曲元系统和局部位移测量系统的GDS应力路径三轴测试系统,研究了小应变范围内应力路径转角θ对剪切模量衰减曲线以及阈值剪应变(γ_0.7)的影响。试验结果表明,土体的初始剪切模量G₀值与初始固结应力大小呈正相关关系,并可表示为与孔隙比e、平均有效应力p′相关的函数关系式。土体的剪切模量在10^-6~10^-3的应变范围内随着剪应变的增加而逐渐衰减,并表现出和试验应力路径与近期应力历史间夹角θ的相关性:应力路径对衰减曲线的影响随着应力路径转角θ的增大逐渐增大,当两者完全相反时,其影响最大。在K₀固结条件下,应力路径转角θ对γ_0.7的影响大于初始固结平均有效应力p′,同时γ_0.7值随着应力路径转角θ的增大而逐渐增大。     

Span length between bearing walls in prefabricated row housing— Architectural and economic aspects

This paper presents a method for the optimal determination of dimensions for prefabricated housing components. The method is based on architectural possibilities on the one hand, and the economic analysis of its implication on the other. The method is demonstrated as a practical application to the determination of span length between transverse bearing walls in prefabricated row housing.

Three types of span length are chosen for the investigation. They are : small (one room), medium (group of rooms) and large (apartment) sizes. The use of these sizes and their combinations are further analysed.

It is concluded that from architectural considerations two possible solutions can be used:

1. (1) The use of small, medium and large span length together in the same apartment, which enables maximum flexibility in design and in use.

2. (2) The use of small and medium combination which provides high flexibility in design of building and apartment and also flexibility in the future; in use, alternation and expansion.

It is also found that the cost of building increases with the increase of span length. If the relative total cost of building construction is 100% for the small span length, medium and large span lengths are 103% and 117%, respectively.

The use of span length combination (in the same building or apartment) has definite architectural advantages. However, it creates technological problems, which result from the use of different floor slab technology, relating to the different spans. Also, the combination of the different spans requires the use of the same floor slab thickness for the different spans, which does not always comply with the structural needs. The economic effects of this are secondary (increase of only 2.5%, with respect to small span only) with the use of small and medium span combination; but quite significant with respect to the cost of the use of small, medium and large floor slab combinations.     

塑料管材在给排水领域的发展及应用

就目前国内常用的给排水塑料管材做了探讨,详细介绍了塑料管材在我国的发展以及各种塑料管材的性能和特点,并指出随着科技的发展,塑料管材在给排水管道工程中的应用将越来越广泛。