International Concrete Abstracts Portal

The present study is an experimental investigation into the performance of high-strength concrete (HSC) square short columns subjected to biaxial bending moments and strengthened by FRP laminates. The main objectives of the study are: to evaluate the strength and deformational enhancement in the structural performance of HSC columns subjected to small biaxial eccentricity when strengthened by externally applied FRP laminates, and to investigate the optimum arrangement and amount of FRP laminates to achieve potential enhancement in structural performance. The study parameters are the number, type and arrangement of FRP layers and the concrete compressive strength. The static axial load small eccentricity (compression-controlled failure) is kept constant corresponding to e/t = 0.125 in two perpendicular directions to the columns principal axes, and the FRP wraps are applied in single or double layers (partial or full column height wrapping). In the present work, test results of eight large-scale concrete columns are presented and discussed. The study has experimentally proven the efficiency of FRP laminates, as a strengthening alternative, in enhancing the strength of biaxially loaded square HSC columns through increasing their axial load carrying capacity (by up to 28%) and flexural capacity (by up to 41%). FRP wraps are also successful in increasing ductility of the strengthened columns. FRP wraps significantly reduced stiffness and strength degradation of HSC columns. Stiffness of strengthened columns is not increased which may be considered an advantage in seismic applications.

The advancement of material technology has led to higher grades of both concrete and steel strengths. High-strength concrete and steel can decrease the size of structural members and increase the available floor area. In addition, it can decrease the consumption of aggregate and steel, promoting environmental sustainability. This research investigates the shear behavior of high-strength reinforced concrete columns under low axial load. The specified compressive strength of concrete is 70 MPa or 100 MPa. The specified yield strengths of longitudinal and transverse reinforcement are 685 MPa and 785 MPa, respectively. Eight large-scale column specimens were constructed and tested in double bending under lateral cyclic load. Test results showed that all specimens had shear failure without yielding of longitudinal reinforcement as expected in design. Higher concrete compressive strength, higher axial load and smaller spacing of transverse reinforcement resulted in higher shear strength. The peak applied load was reached before yielding of transverse reinforcement. The critical shear crack angle was approximately 30° and 20° for columns with 10% and 20% axial load, respectively. The simplified shear strength equation of the ACI 318 code was conservative for columns tested in this research and for high strength columns collected from literature. However, the detailed shear strength equation exhibited non-conservative results for most of the columns examined.

CRC, short for Compact Reinforced Composite, is an ultra high performance fiber reinforced concrete developed by the Danish cement producer Aalborg Portland in 1986. CRC has very high compressive strength combined with a large volume of steel fibers, which also gives the material improved tensile capacity and toughness. These properties make CRC ideal for use in the blast-resistant design of structures. This research study presents the results of an experimental program examining the blast performance of UHPFRC columns constructed with CRC. Six half-scale columns were tested under simulated blast loading using state-of-the art shock-tube testing facilities at the University of Ottawa. Two specimens were constructed with traditional concrete (SCC was used to facilitate placement) and four specimens were constructed with CRC. The test parameters included concrete type (SCC and CRC), transverse reinforcement spacing (non-seismic and seismic detailing) as well as fiber content (2%, 4% and 6% for the CRC specimens). The results show that ultra-high performance concretes such as CRC improve the blast performance of columns in terms of maximum and residual displacements. In addition the use of CRC results in marked improvements in terms of damage tolerance and elimination of secondary blast fragments. Furthermore, the results demonstrate that the use of seismic detailing in both traditional concrete and CRC specimens improves blast performance. Finally the paper demonstrates that the use of single-degree-of-freedom (SDOF) analysis can be used to predict the blast response of CRC columns with reasonable accuracy.

Application of high performance materials in construction combines the advantages of reducing the use of materials, cross-section and reinforcement congestion. Although the application of high strength concrete (HSC) has been gaining popularity in high-rise building construction, parameters affecting the performance of HSC members are still under investigation. The use of high strength steel can result in reduced steel congestion and low cost associated with transportation and installation of rebars. Although many design codes and guidelines apply restrictions on the yield strength of steel reinforcement, high-strength steel (HSS) rebars are still a viable option for longitudinal reinforcement in columns of multi-story moment-frame buildings designed to resist earthquake motions. In this study, a numerical approach has been undertaken for the seismic fragility analysis of RC columns and frames with HSS and HSC. Fragility curves provide the flexibility to deal with the uncertainty in geometric properties, along with the typical uncertainties such as material and ground motion uncertainties. Latin Hypercube Sampling (LHS) technique is employed to quantify the uncertainties associated with different modeling parameters such as concrete compressive strength, yield strength of longitudinal and transverse reinforcement, gross geometries and ground motions. Probabilistic seismic demand model (PSDM) is used to develop fragility curves. The fragility curves thus developed quantify the vulnerability of high strength RC columns and frames and show their effectiveness in reducing the probability of failure compared to regular strength RC columns.

National Research Council Canada has recently upgraded its column furnace facility for assessment of columns in fire under not only the applied axial loads but also a potential lateral load. The main goal for this upgrade was to be able to simulate lateral displacement of columns during the fire due to thermal expansion of slabs/floors and to assess a column’s residual seismic/lateral load capacity after fire damage. Furthermore, the new column facility enhancement included a hybrid testing technology in which the column could be tested considering its structural interactions with the remaining of the structure. This paper includes the summary of the new upgrade and testing technology; however, more focus will be on the structural response of a high strength column, with steel fibre, tested using the new upgrade and approach. This includes the fire test of the high strength column specimen as well as lateral load test of the column to determine its residual lateral resistance with fire damage. The results of these tests revealed that fire substantially reduced the residual lateral load/displacement capacity of the high strength concrete column. The new commissioned testing technique/tool could assist researchers to seek and find solutions for more reliable post-fire structural inspection and to develop design tools for the mitigation.