Research
Size Effect in Reinforced Concrete
How reliably can we translate findings from reduced-scale laboratory tests to larger structures for design?
Most laboratory tests are conducted on a reduced scale, from which suggestions are made for much larger real structures. However, in translating the results from small-scale elements to larger counterparts, one has to consider the "Size Effect." The size effect reduces the normalized nominal strength of members compared to their experimental small-scale replicas. In lay terms, it would mean that the strength of smaller lab specimens would be higher than that of their up-scaled replicas in practice. This is important for design, as design equations are based on experimental data heavily comprised of small-scale tests. Thus, quantifying strength reduction with size effect is an important scientific problem. In some cases, the size effect would not significantly impact the design as the lower strength may already have been accounted for through either strength reduction and/or load amplification factors. However, this remains an issue to be considered separately in particularly large-sized specimens. To quantify the size effect in two-way shear members, an experimental plan consists of twelve total pile cap specimens and three specimens each at different scales (1x, 2x and 4x). The largest set of four specimens were 1250mm thick; the next set consisted of four pile caps with 625mm thickness, which is half their larger counterparts; and the smallest set of four specimens were further halved in size. Observed results were compared with the size effect provisions from American and Japanese codes, and necessary recommendations were made. A brief visual summary can be found below.
Most laboratory tests are conducted on a reduced scale, from which suggestions are made for much larger real structures. However, in translating the results from small-scale elements to larger counterparts, one has to consider the "Size Effect." The size effect reduces the normalized nominal strength of members compared to their experimental small-scale replicas. In lay terms, it would mean that the strength of smaller lab specimens would be higher than that of their up-scaled replicas in practice. This is important for design, as design equations are based on experimental data heavily comprised of small-scale tests. Thus, quantifying strength reduction with size effect is an important scientific problem. In some cases, the size effect would not significantly impact the design as the lower strength may already have been accounted for through either strength reduction and/or load amplification factors. However, this remains an issue to be considered separately in particularly large-sized specimens. To quantify the size effect in two-way shear members, an experimental plan consists of twelve total pile cap specimens and three specimens each at different scales (1x, 2x and 4x). The largest set of four specimens were 1250mm thick; the next set consisted of four pile caps with 625mm thickness, which is half their larger counterparts; and the smallest set of four specimens were further halved in size. Observed results were compared with the size effect provisions from American and Japanese codes, and necessary recommendations were made. A brief visual summary can be found below.
Hysteretic Modelling for Reinforced Concrete Members
Could we take advantage of available test data to predict the complex hysteretic behaviour of RC members?
Hysteretic Modelling for Reinforced Concrete Members. Could we take advantage of available test data to predict the complex hysteretic behaviour of RC members? In structural analysis, especially in the case of seismic loading, it is essential to model both capacity curves and the hysteretic behaviour of each member carefully. Hysteretic modelling is generally a complex task involving predicting different loading-unloading cycles at different drift levels. Moreover, different parametric configurations must be considered for accurately estimating hysteretic behaviour, just as they are accounted for in capacity predictions. Using the hysteretic test data from 113 columns and 108 walls, equations for pivot parameters α and β capturing the influence of key parameters were proposed. Calibration of these equations was carried out to minimize the differences in predicted vs experimental total energy dissipations of hysteretic curves. For this complex optimization problem, a metaheuristic algorithm titled "simulated annealing" was used to escape local minima while arriving at global minimums. Notable hysteresis differences in shear versus flexure, such as more significant pinching in shear, were accurately captured. These results made it possible to carry out accurate nonlinear time history analyses that result in reliable global predictions.
Hysteretic Modelling for Reinforced Concrete Members. Could we take advantage of available test data to predict the complex hysteretic behaviour of RC members? In structural analysis, especially in the case of seismic loading, it is essential to model both capacity curves and the hysteretic behaviour of each member carefully. Hysteretic modelling is generally a complex task involving predicting different loading-unloading cycles at different drift levels. Moreover, different parametric configurations must be considered for accurately estimating hysteretic behaviour, just as they are accounted for in capacity predictions. Using the hysteretic test data from 113 columns and 108 walls, equations for pivot parameters α and β capturing the influence of key parameters were proposed. Calibration of these equations was carried out to minimize the differences in predicted vs experimental total energy dissipations of hysteretic curves. For this complex optimization problem, a metaheuristic algorithm titled "simulated annealing" was used to escape local minima while arriving at global minimums. Notable hysteresis differences in shear versus flexure, such as more significant pinching in shear, were accurately captured. These results made it possible to carry out accurate nonlinear time history analyses that result in reliable global predictions.
Shear Capacity Estimation in Reinforced Concrete
Lateral strength of structural walls & punching strength of pile caps and flat plates & shear strength of beam-column joints
Broadly, member failures can be classified into either flexure or shear. Several engineering assumptions made it possible to provide flexural capacity estimations with reasonably good confidence. Flexure-dominant members are also desired in design for their ductile responses. However, some types of members are inherently shear-dominant, and their failure is brittle. Thus, shear strength estimation is an area of great interest to researchers and designers. More complex tools, such as strut-and-tie models, are commonly adopted. Based on the available test data, suitable force transfer mechanisms were derived for structural shear walls with openings (for windows) consistent with observed failure crack patterns. In addition to shear walls, the punching behaviour of pile caps (with nonsymmetric pile configurations) and flat plates (with and without shear reinforcement) were studied to propose models that reliably predict their strength. These analytical models helped provide reliable estimates and advocated for improved design recommendations in state-of-the-art standards for RC design.
Broadly, member failures can be classified into either flexure or shear. Several engineering assumptions made it possible to provide flexural capacity estimations with reasonably good confidence. Flexure-dominant members are also desired in design for their ductile responses. However, some types of members are inherently shear-dominant, and their failure is brittle. Thus, shear strength estimation is an area of great interest to researchers and designers. More complex tools, such as strut-and-tie models, are commonly adopted. Based on the available test data, suitable force transfer mechanisms were derived for structural shear walls with openings (for windows) consistent with observed failure crack patterns. In addition to shear walls, the punching behaviour of pile caps (with nonsymmetric pile configurations) and flat plates (with and without shear reinforcement) were studied to propose models that reliably predict their strength. These analytical models helped provide reliable estimates and advocated for improved design recommendations in state-of-the-art standards for RC design.
