International Concrete Abstracts Portal

When insulated concrete sandwich panels are used in the envelope of a building, the experior and interior are subjected to two different environments. The exterior concrete wythe is subjected to outside weather swings in the temperature and humidity causing thermal expansion and contraction, whereas the interior is exposed to a controlled steady room temperature environment. Dimensional change in the panel depends primarily on the height of the panel and the relative change in temperature. The severity increases when the outside concrete wythe of a tall panel is supported (and hence constrained) on the foundation dlowing vertical movements only at the top. If these weather cyclic movements are restricted, the panels may experience cracking and eventually may experience a premature failure. Therefore, the tie system used in the panels should be flexible enough to accommodate these differential movements. This often is the most critical issue in the service life of the building when sandwich panels are used. There is no standard test method available to evaluate the thermal non-uniform cyclic behavior of insulated panel systems. The authors have followed a sci- entific approach to evaluate these stresses by subjecting the ties to real life cycles occurring over a period of time. The system used in this study includes a low-conductivity polymer connector with extruded polystyrene rigid foam insulation. The testing was continued until the failure of the system or to more than 100 years of equivalent cycling (the expected service life of the building), whichever is less. This paper focuses on the methodology developed and parameters considered in developing the criteria for testing weather cycles. The procedure may be followed to evaluate any given insulated panel system to predict its long-term durability.

The objective of this paper is $to introduce an innovative sandwich wrapping confining system (SWCS) for upgrading and repairing rectangular columns. The system described here replaces the conventional fiber reinforced polymer (FRP) wrapping, which has only axial stiffness, by a sandwich wrapping confining system that has both axial and flexural stiffness. The new system is made up of two FRP faces separated by a light incompressible core. Experimental and numerical analyses are performed on rectangular columns upgraded and repaired using the SWCS. Thuty rectangular columns with different dimensions are upgraded and repaired using the SWCS and tested to failure. A numerical study based on nonlinear finite-element analysis (material nonlinearity) is used to investigate the behavior of the columns repaired using the SWCS and to predict the experimental failure loads. Finally, the experimental and the analytical results are compared. Unlilce conventional FRP jackets, the SWCS can be used to improve the strength, stiffness, and ductility of rectangular columns.

The performance of beam-to-column connections subjected to reversed cyclic loading depends on several variables. In this investigation, the effects of eccentric spandrel beams, wide normal beams, column section aspect ratio, loading in two principal directions, and slab participation on the inelastic behavior of beam-to-column connections are studied. The experimental program features three 3/4-scale exterior reinforced concrete beam-column-slab subassemblies. The major design variables for the specimens are the eccentricity of the spandrel beam with respect to column, beam and column section aspect ratios, and joint shear stress level. Results of the experimental program, including load-displacement response, beam plastic hinge rotation, joint distortion, and bond deterioration are presented in this paper.

During concrete construction, form oil, bond breaker, concrete splatter and other types of contaminants often contaminate reinforcement. Current specifications and quality control measures require the removal and clean up of these contaminants before the placement of concrete due to a concern of a reduction in bonding capacity. This is costly, labor intensive, and may not be necessary. Currently, there is limited research on the effect of reinforcing bar contami- nation on the bond between the deformed steel reinforcing bar and concrete. Because of this lack of data, specifications are conservative and require the removal of the contaminant. Inspectors often cite ACI 301-96, Standard Specifications for Structural Concrete, which states, When concrete is placed, all reinforcement shall be free of materials deleterious to bond. If it could be conclusively proven that this level of care is unnecessary, the construction industry would benefit greatly. To address the effects of contaminants on bond characteristics of deformed steel reinforcing bars, a preliminary study was completed at the University of Missouri-Rolla. The research program focused on three contaminants often seen during construction: form oil, bond breaker and concrete splatter. Other variables included size of reinforcing bar, strength of concrete and epoxy versus uncoated reinforcing bar. This paper will provide the experimental program and test procedures as well as the test results and observations. The results weal that in the majority of situations tested, the ultimate bond stress was not significantly affected by the three contaminants tested. In some cases, the bond breaker and form oil affected the smaller epoxy coated bars, while the effect of concrete splatter was insignificant.

Recent European and UK policies, for example the Landfill Duecave and the UK landfill tax, have set an agenda to promote reuse and recycling by con-trolling and minimising the landlilling of secondary materials. The UK Govern- ment and it’s agencies are actively pursuing policies of sustainable and environ- mentally responsible construction. The changing attitute towards secondary materials has encouraged investigation into the use of ferro-silicate slag from the Imperial Smelting Furnace (ISF) production of zinc in construction processes. The UK Ten Year Transport Plan, including the development of the highway infrastructure, offers opportunities to successfully demonstrate the consumption of small volume streams of secondary materials, including ISF slag, within the local area. Pavement construction offers several opportunities for consumption, the most credible of these being the replacement of the sand fractions by the slag in bound mixtures, cement and bituminous. This paper focuses upon cementitious mixtures alone. The presence of zinc and lead ions in the ISF slag are proven to have an impact on the setting characteristics of concrete mixtures, although there is little difference in the compressive strengths after 28 days. The leaching, characteristics of the slag suggest that the retardation is not linearly related to the quantities of zinc or lead leached. Additiwuilly, leaching tests in combination with pulverised fuel ash (fly ash) and ground granulated blastfurnace slag indicate that it may be possible to minimise retardation of set in by including these materials in the concrete mixture.

Cracking in concrete is fundamentally altered by the addition of reinforcing fibers. A combination of microfibers (less than 22 pi [0.0oO9 in.] in diameter) and macrofibers (500 p.m 10.0197 in.] in diameter) that contribute in comple- mentary ways to performance, is presented as a means for controlling cracking and improving the lifecycle behavior of concrete. In previous work, a hybrid blend of these fibers in a mortar matrix demonstrated better mechanical performance and lower cracked permeability than was seen with a single fiber type. The research presented in this paper attempts to realize the potential of such blends in concrete. A mixture proportioning method that achieves good workability and cohesion in concretes containing microfibers was used to produce a cast concrete. The mechanical performance and shrinkage cracking resistance of this material were evaluated. In the hybrid reinforced concrete, the microfibers delayed the development of macrocracks and so the composite demonstrated greater strength and cracking resistance than a similar matrix reinforced with macrofibers only. However, this influence was less pronounced than was observed with a mortar matrix and was confined to smaller crack openings.

This paper examines the effectiveness of nodinear static procedures for seismic response analysis of buildings. Nonbm static procedures are recom- mended in FEMA 273 (Federal Emergency Management Agency-Guidelines for Seismic Rehabilitation of Buildings) for assessing the seismic performance of buildings for a given earthquake hazard representation. Three nonlinear static procedures specified in FEMA 273 are evaluated for their ability to predict defonnation demands ia terms on inter-story drifts and potential failure mechanisms. Two steel and two reinforced concrete buildings were used to evaluate the procedures. Strong-motion data recorded during the Northridge,earthquake are available for these buildings. Tfie study shows that nonlinear static procedures are not effective in predicting inter-story drift demands compared to nonlinear dynamic procedures. Nonlinear static procedures were not able to capture yielding of columns in the upper levels of one of the sekted buildings. This inability can be a sienificant source of concern in identifying local upper story failure mechanisms.

The basic problem in beam-column design is to establish the proportions of a reinforced concrete cross-section whose design strength is just adequate enough to support the factored axial load and moments. Since the stress distribution due to the axial load and moment depends on the cross-section’s proportions, which are initially unknown, column design cannot be carried out directly. Instead, the proportions of a cross-section must be estimated and then investigated to determine whether its design capacity is adequate for the factored loads and moments. The dimensions of a beam-column cross-section and the area of reinforcing steel required to support a specific combination of axial load and moment can be established by using the column design interaction curves, where an interaction curve represents all possible combinations of axial load and moment that produce failure of the cross-section. The bending resistance of an axially loaded column about a particular skewed axis due to biaxial moments can be determined through itera- tions and lengthy calculations. These extensive calculations are multiplied when optimization of the reinforcing steel or column cross-section is required. This pa- per investigated the suitability of an Artificial Neural Network (ANN) for model- ing a preliminary design of reinforced concrete beam-column. An ANN back- propagation model has been developed to design a beam-column which predicts column cross-section and reinforcing steel requirements for a given set of inputs which are concrete compressive strength, reinforcing steel strength, factored axial load and moment. The trained ANN back-propagation model has been tested with several actual design data, and a comparative evaluation between the ANN model predictions and the actual design has been presented.

The benefits derived from the ability of the fibers to control crack propagation have been recognized for many years. In addition, the development of high-perfurmance concretes has enhanced this situation as the increases in strength lead to a more brittle behavior of the material. The introduction of steel-fiber rein- forcement in these concretes is probably the best way to improve the performance of concrete when higher tenacity is required. This paper shows the contribution of fiber reinforcement in both conventional and high-strength concretes exposed to temperatures up to 500°C. Conuutes with diffemnt types and content of fibers are analyzed, mainly regarding the failure mechanism and tenacity. The post-peak behavior under conpressive and flexural loads is studied using a close loop system. NDT was also used to evaluate the damage. The residual mechanical properties of fiber-reinforced concretes qre affected in a similar way thau those corresponding to plain concrete. Nevertheless, it can be seen that the residual parmeters tend to increase as the strength increases when high carbon-steel fibers bstead of low carbon-steel fibers are used, and when fiber reinforcement is introduced.

Imaging and non-imaging sensors that collect spectral data of surface materials are rapidly becoming available to engineers due to advances in electrooptics and sensor technology. Applications of remote sensing for the identification of surface materials and determination of some of their characteristics have been developed in the geological sciences. Transportation research systems are moving aggressively towards using these types of technologies for materials such as soil subgrades, concrete, asphalt, and, to a lesser extent, steel. A series of experiments were identified to analyze the spectral response of laboratory prepared surfaces, primarily of materials with a mineralogical origin, including soil, aggregate, and concrete. This paper presents the experimental procedure and results of a series of tests performed on a mortar mixture. Temperature, strength, and spectral reflectance were measured for a period of time during curing of the mortar. Results revealed apparent correlations between temperature, water content (curing rate), and spectral response.