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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.
The paper presents observed damage in reinforced concrete buildings during the 27 February 2010 Maule earthquake in Chile. Performance of concrete frame and shear wall buildings are discussed with emphasis on seismic deficiencies in design and construction practices. It is shown that the majority of structural damage in multistorey and high-rise buildings can be attributed to poor performance of slender shear walls, without confined boundary elements, suffering from crushing of concrete and buckling of vertical wall reinforcement. Use of irregular buildings, lack of seismic detailing, and the interference of nonstructural elements were commonly observed seismic deficiencies. A comparison is made between Chilean and Canadian design practices with references made to the applicable code clauses. Lessons are drawn from the observed structural performance.
Seismic vulnerability assessment of shear wall buildings can be conducted through non-linear dynamic analysis, which requires detailed analytical modeling, the consideration of different earthquake intensity and structural performance measures. Reinforced concrete shear wall buildings were designed for Vancouver, representing a region of high seismicity in Canada, to assess seismic vulnerability of buildings constructed before and after the enactment of modern seismic design codes. The buildings either had a two-storey or a five-storey height, designed either using the 1965 or the 2010 National Building Code of Canada. Analytical models were generated for non-linear response time history analysis using computer software PRFORM-3D. Fiber-discretized sections were used for flexural response based on constitutive models for concrete and reinforcing steel. The nonlinear behavior in shear was modelled on the basis of sectional non-linear shear response. The shear wall models were validated against experimental data available in the literature before incremental dynamic analysis (IDA) was employed to generate fragility curves. Spectral acceleration at the fundamental period was used as seismic intensity parameter and inter-storey drift of the first floor was selected as the damage indicator. Performance limits considered include Immediate Occupancy, Life Safety and Collapse Prevention. The resulting fragility curves indicate that the life safety intent of the 2010 building designs has been met, while the same requirements could not be satisfied for the 1965 building designs.
Strengthening of concrete structures using fiber-reinforced polymer (FRP) systems has become a widely accepted technology in the construction industry over the past decade. Externally bonded FRP sheets are proven to be a feasible alternative to traditional methods for strengthening and stiffening deficient reinforced or prestressed concrete members. However, the delamination of FRP sheets from the concrete surface poses major concerns, as it usually leads to a brittle member failure. This paper reports on the development of FRP anchors to overcome delamination problems encountered in surface bonded FRP sheets. An experimental investigation was conducted on the performance of carbon FRP anchors that were embedded in normal- and high-strength concrete test specimens. A total of 81 anchors were tested under monotonic uniaxial loading. Test parameters included the length, diameter, and angle of inclination of the anchors and the compressive strength of the concrete. The experimental results indicate that FRP anchors can be designed to achieve high pullout capacities and hence can be used effectively to prevent or delay the delamination of externally bonded FRP sheets. The results also indicate that the diameter, length, and the angle of inclination of the anchors have a significant influence on the pullout capacity of FRP anchors.
Abstract This research has investigated the effect of reinforcement corrosion on the flexural response of reinforced concrete beams subjected to blast loading. Five beams, with and without corrosion, were tested under blast loads using a shock‐tube. The corroded specimens were subjected to an accelerated corrosion regime prior to testing, with a mass loss of up to 22% in the longitudinal steel reinforcement over the mid‐span or full‐span regions. A companion set of two beams was tested under quasi‐static four‐point bending. The results from the static tests show that corrosion of the longitudinal reinforcement decreased the strength and ductility, and ultimately changed the failure mode from ductile to brittle. Under blast loading, the steel corrosion increased maximum displacements and support rotations, reduced blast capacity, increased damage and fragmentation, and led to more brittle failure as the % mass loss increased. The effects of corrosion on blast response were moderate when the steel was corroded over the full‐span region. Furthermore, the blast response of the beams was predicted using dynamic inelastic single‐degree‐of‐freedom (SDOF) analysis, with the resistance functions developed using 2D finite element modeling, while accounting for the reduction in steel stress–strain properties and corrosion‐induced cracking. The SDOF analysis showed acceptable results in terms of ability to predict maximum displacements of the flexural‐governed beams (corroded and un‐corroded).
Fiber reinforced polymer (FRP) reinforcement, in the form of longitudinal bars and transverse grids is currently being developed for use in new building and bridge structures. However, FRP reinforcement shows linear stress-strain characteristics up to failure, without any ductility. Experimental research is currently conducted at the Structures Laboratory of the University of Ottawa to investigate the seismic performance of FRP reinforced concrete structural elements. Large scale columns and beams are being tested under simulated seismic loading. The results of selected tests are summarized in this paper, with the assessment of their significance from seismic performance perspective. Specimens representing part of a first storey building column between a footing and the point of inflection; and the portion of a beam between a column and the point of inflection, were tested under lateral deformation reversals. The members were reinforced with carbon FRP bars in the longitudinal direction, and carbon FRP grids in the transverse direction. Both the columns and the beams sustained a minimum of 2% to 3% lateral drift ratios, meeting seismic drift limitations of most building codes. Test results indicate that FRP reinforced concrete elements exhibit reduced stiffness and softened response, when compared with conventional steel reinforced concrete elements, because of the lower elastic modulus of FRP bars. This may suggest reduced spectral values associated with longer vibration periods, as well as increased deformability, resulting in seismic resistant structures for which elastic design approach with sufficient deformability may be appropriate.
Computer software was developed for inelastic analysis of structural members subjected to blast-induced shock waves. The software can predict the dynamic response of structural elements, provided the load–deformation characteristics are defined. The software has built-in capabilities to generate the load–deformation characteristics of common structural and non-structural members. Currently this capability includes reinforced concrete columns, one-way walls, beams, and one-way slabs. The input consists of member geometry, boundary conditions, dynamic material properties, explosive threat parameters, and desired performance levels. The results are presented in graphical format in terms of structural load–deformation characteristics, single degree of freedom displacement – time histories and iso-displacement pressure–impulse diagrams. The program was verified extensively using experimental data generated from simulated explosive loading of reinforced concrete members at the University of Ottawa shock tube testing facility. The shock tube has been shown to generate a wide range of pressure–impulse combinations, accurately simulating free-field detonation of high explosives of various mass and standoff distances.
Modelling the expansion and damage generated by alkali–aggregate reaction (AAR) in reinforced concrete structures is quite complex, yet necessary to obtain accurate predictions of the structural response of distressed members. Several AAR models have been developed to predict expansion and damage at the material (microscopic) or the structural (macroscopic) scales. However, those models tend to either neglect or overemphasise the critical physicochemical parameters of the reaction, which limits their applicability. Therefore, a new simple yet reliable finite-element approach is proposed to fill this gap. It accounts for the most important parameters affecting AAR through an engineering approach, without the need for non-technical guesses or to ‘fit’ model parameters. The proposed model is validated through the computational simulation of reinforced concrete specimens cast and monitored in the laboratory. Results show that AAR expansion was accurately simulated by accounting for the anisotropic (stress state dependent) nature of the reaction, mechanical properties deterioration and an analytical equation capable of representing AAR's free expansion. Next steps include validating the approach by simulating real structures and incorporating phenomena like leaching and combined distress mechanisms.
Experimental research was conducted to investigate the behavior of square high-strength concrete columns confined by rectilinear reinforcement. Large-scale columns with concrete strengths between 60 MPa and 124 MPa were tested under monotonically increasing concentric compression. The test parameters included the volumetric ratio and spacing of transverse reinforcement, distribution of longitudinal reinforcement and resulting tie arrangement, yield strength of transverse reinforcement, and concrete compressive strength. The results indicate that high-strength concrete columns can be confined to achieve inelastic deformabilities usually expected of normal-strength concrete columns. This is done by providing increased volumetric ratio and/or higher grade of confinement reinforcement. The results of the experimental program are presented in the paper, along with recommendations for design.
Masonry infill walls are often used as non-structural elements. According to the past structural failure, ignorance of interaction between infill walls and enclosed frame may lead to the different seismic response for non-ductile building frames. The main contribution of this paper is to analytically investigate the behavior of reinforced concrete with masonry infill panels as participating structural. In doing so, a finite element model based on an equivalent strut method is conducted to represent the behavior of masonry panels. The strut model is calibrated using the results of the companion experimental program, which examined the cyclic behavior of infill panels with and without FRP sheets. Accordingly, a nonlinear spring element and a shell element are used to simulate the behavior of masonry strut elements and FRP sheets, respectively. The nonlinear static analysis (Push over analysis) is accomplished using SAP2000 [1] structural analysis software for a 10-story building with FRP sheets subjec
Behavior of high-strength concrete columns with concrete strengths of up to 90 MPa was investigated experimentally. Large-scale columns were tested under different levels of constant axial compression and incrementally increasing lateral deformation reversals. The columns had a circular cross section and circular transverse reinforcement. Different volumetric ratios and grades of steel were used to confine the core concrete. The results indicate that the deformability of high-strength concrete columns can be improved significantly through confinement. Inelastic drift capacity of columns can be improved to levels well beyond those usually expected during strong earthquakes. The improvements can be achieved with volumetric ratios of confinement steel that are typically used for normal-strength concrete columns, provided that higher grades of steel are used. Furthermore, analytical techniques commonly employed for analysis of normal-strength concrete columns can also be used for high-strength concrete columns, if proper material models are incorporated, reflecting stress-strain characteristics of high-strength concrete and reinforcing steel.
An analytical procedure was developed to predict the compression membrane behavior of laterally restrained reinforced concrete members subject to extreme loads, such as those generated by the loss of bearing elements or during the application of excessive lateral loadings (e.g., explosions and impact). The procedure is based on the simplifying assumption that flexure and arching calculations can be uncoupled and that beam growth due to flexure after cracking can be approximated using rigid body rotation of beam half-segments. A lumped inelasticity flexure analysis is first performed to determine the degree of contact between the beam end and lateral support. The arching contribution to load capacity is computed by considering equilibrium of the contact zone arising from the projection of the beam into a partially rigid support. The total compression membrane strength is taken as the superposition of flexure and arching strength components. The methodology can handle supports with both rigid and nonrigid lateral restraint and varying degrees of rotational fixity. The numerical procedure has been verified extensively against the results of laterally restrained beam-column assembly and slab tests reported in the literature. The methodology can be used to model arching action under quasi-static conditions, or for inelastic dynamic analysis of structures subjected to blast and impact, provided high strain rate material properties are incorporated.
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Large scale high-strength concrete columns were tested under simulated seismic loading. The columns had either a square or a circular cross-section with 104 MPa or 90 MPa concretes, respectively. The test parameters considered included the volumetric ratio, grade and arrangement of transverse reinforcement. The columns were subjected to constant axial compression and incrementally increasing lateral deformation reversals. The results are presented in the form moment-displacement hysteretic relationships and indicate that high-strength concrete columns can be confined to possess inelastic deformabilities usually expected of normal-strength concrete columns. However, high-strength concrete columns do require higher lateral pressure, provided either by increased volumetric ratio or higher grade of transverse reinforcement. The effectiveness of high-strength transverse reinforcement depends on the efficiency of confinement reinforcement and the level of axial compression. Circular columns and square columns with closely spaced transverse and longitudinal reinforcement show superior performance when high-strength steel is used to confine concrete. The use of higher grade transverse steel in these columns permit a reduction in the volumetric ratio, without reducing column deformability.
