252 publications from this institution
Strength and ductility of high-strength concrete columns were investigated by examining available test data. The results are summarized in terms of load and ductility capacities of columns. Experimental observations indicate that strength and ductility of high-strength concrete columns can be improved to levels that are usually expected of normal-strength concrete columns, provided that the core concrete is adequately confined by transverse reinforcement.
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Analytical and experimental research was conducted to develop a design procedure for seismic retrofit of existing circular concrete columns using carbon fiber reinforced polymer (CFRP) jackets. The analytical research is an extension of earlier work on the development of a displacement based design procedure for column confinement. The experimental work involves full-size bridge columns tested under simulated seismic loading, consisting of constant axial compression and incrementally increasing lateral deformation reversals. The specimens are representatives of typical bridge columns between the footing and the point of inflection. One of the columns tested represents as-built conditions in practice with longitudinal reinforcement spliced near the base, providing an assessment of the deformability of existing columns. The test results indicate that the deformability of this column is limited to 1% lateral drift ratio. Companion columns with identical properties and CFRP jackets show that the deformability can be improved significantly through jacketing. CFRP jacketing of circular columns is effective in improving bond between reinforcement and concrete within the plastic hinge region while also confining the compression concrete. The lateral deformability of retrofitted columns shows improvements beyond 5% drift ratio. It is shown that columns satisfying the proposed design expressions develop ductile behavior, meeting the performance criterion adopted in design.
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Freezing and thawing cycles (FTC) on RC columns are a significant problem for vulnerable infrastructure exposed to extreme climate conditions. This problem is exacerbated by the presence of deicing agents that lead to reinforcement corrosion and overall concrete deterioration. Current research has mainly focused on studying the mechanical properties of concrete when exposed to cyclic conditions of freezing and thawing. Few studies have analyzed FTC’s influence or the dual action of FTC and steel corrosion on the structural performance of RC. This paper surveys available literature on the synergistic effects of one or multiple environmental exposures on RC columns and methodologies for inducing frost damage according to current standards. The literature survey is organized as follows: (1) frost damage mechanism; (2) test methods to evaluate frost damage; (3) effect of FTC on concrete mechanical properties; (4) effect of FTC on the structural performance of RC columns; and (5) effect of dual action of FTC and steel corrosion on RC columns. Finally, this paper draws a series of conclusions and recommendations for future work.
No abstract is provided for this article.
The Adhesive-Applied Roofing System (AARS) is a new generation of built-up roofs gaining popularity in North American low-slope application. AARS uses no fasteners, and all components (e.g., steel deck, vapor barrier, insulation board, cover board, and membrane) are integrated by application of adhesives. Although AARS has been in use, existing standards address only mechanically attached or bonded roof assemblies. To quantify the wind-uplift performance of the AARS, an industry–university–government collaborative research project, Development of Wind Uplift Standard for Adhesive-Applied Low-Slope Roofing System, has been initiated. The project has three major tasks: experimental investigation, formulation of a numerical model, and development of wind design guide and standards. Task 1 developed test protocols to quantify the uplift and peel resistance of small-scale AARS specimens respectively subjected to tensile and shear loading. Using the standardized tensile test parameters, this paper identifies the effect of material combinations and variation in the adhesive applications on the uplift resistance of AARS subjected to tensile loading. This parametric study not only verified the applicability of the developed tensile test method for variations in the configurations, but it also identified the weakest link in AARS. Data from this small-scale testing can facilitate industries to optimize the material combinations such that it can be correlated with the systems wind uplift resistance.
Two discussions of a paper with the aforementioned title by J. Hoshikuma, K. Kawashima, K. Nagaya, and A.W. Taylor, published in this journal (Volume 123, Number 5, May 1997), are presented. The first discusser presents a model that he proposed in 1991, which was developed on the basis of a large database including 63 column specimens with rectangular hoops from five different experimental programs. He also proposes that the effect of hook shape, the relationship between the strength of the unconfined specimens the authors tested to the cylinder strength, and the possible effect of longitudinal reinforcement warrant further investigation. The last two discussers present eight points that they believe deserve further attention before the authors' approach for confined concrete columns can be utilized. Discussions are followed by closure from the authors.
No abstract is provided for this article.
Observations on damage to concrete structures, due to the 1994 Northridge earthquake, are reported from a Canadian code perspective. Most of the damaged structures were older, nonductile, structures that do not conform to current design and detailing requirements. Concern is expressed about the seismic hazard of older Canadian structures having similar deficiencies. A significant number of parking structures suffered extensive damage and a number of precast concrete parking structures collapsed. Deficiencies in these structures include lack of proper diaphragm connections, a mix of gravity load columns with ductile framing, inappropriate number and distribution of shear walls, torsional effects caused by ramps, and the creation of short columns due to geometric features. This earthquake also demonstrated the deficiencies in connections of pre-1973 tilt-up structures. Key words: seismic design, earthquake, Northridge, structures, codes, concrete, precast concrete.
This paper describes damage to bridges caused by the 1994 earthquake at Northridge, California. A description of the damage and the probable causes are presented for the seven bridges that suffered some form of collapse. The majority of damage was due to column shear or combined shear and flexure failures, but restrainer failure was the cause of collapse in one bridge. The lack of damage to other bridges and to foundations is discussed. Key words: Northridge, earthquake, seismic, bridges, damage, performance.
The proposed 2005 edition of the National Building Code of Canada specifies dynamic analysis as the preferred method for computing seismic design forces and deflections, while maintaining the equivalent static force method for areas of low seismicity and for buildings with certain height limitations. Dynamic analysis procedures are categorized as either linear (elastic) dynamic analysis, consisting of the elastic modal response spectrum method or the numerical integration linear time history method, or nonlinear (inelastic) response history analysis. While both linear and nonlinear analyses require careful analytical modelling, the latter requires additional considerations for proper simulation of hysteretic response and necessitates a special study that involves detailed review of design and supporting analyses by an independent team of engineers. The paper provides an overview of dynamic analysis procedures for use in seismic design, with discussions on mathematical modelling of structures, structural elements, and hysteretic response. A discussion of the determination of structural period to be used in association with the equivalent static force method is presented.Key words: dynamic analysis, earthquake engineering, elastic analysis, fundamental period, hysteretic modelling, inelastic analysis, National Building Code of Canada, seismic design, structural analysis, structural design.
This paper consists of reported information divided into two general categories, performance of High-Strength Concrete (HSC) columns under concentric loads, and combined axial and bending moments. Presented is a brief summary of the highlights of the reported data.
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This paper presents an analytical model developed to predict the flexural load-deformation behavior of reinforced concrete members containing tension lap splices. The proposed model incorporates the effect of reinforcement slip of the lap splice and the effect of high strain rates on bond characteristics and material properties of concrete and steel. The main advantages of the proposed model are that bond-slip phenomena are captured through the use of pseudo-material stress-strain relationships, rather than giving consideration to the continuum of reinforcement and slippage over the entire structural element. Material properties and associated dynamic increase factors (DIF) are defined using accepted formulations. A suitable bond-slip law is presented and modified to account for the influence of strain rates on bond characteristics. Beam failure criteria are expressed in terms of a flexural failure of the member or a bond splitting failure of the splice. A comparison of the analytical predictions with experimental data demonstrated that the proposed analysis technique can reasonably predict the flexural response of beams with tension lap splices. The results also show that the model is equally applicable for use at low- and high- strain rate loading, such as those generated during blast and impact loading.
Simple relationships are proposed in this paper by modifying the Schmertmann's equation for settlement estimations of footings (i.e., <TEX>$B/L{\approx}1$</TEX>) carrying vertical loads in saturated and unsaturated sandy soils. The modified method is developed using model plate load tests (PLTs) and cone penetration tests (CPTs) results conducted in saturated and unsaturated sand in a controlled laboratory environment. Seven in-situ large-scale footings tested under both saturated and unsaturated conditions in sands were used to validate the proposed technique. The results of the study are encouraging as they provide reliable estimates of the settlement of shallow footings in both saturated and unsaturated sands using the conventional CPT results.
