International Concrete Abstracts Portal

Nonplanar reinforced concrete (RC) core walls form the backbone of millions of mid- and high-rise buildings, resisting both gravity and lateral loads from wind and earthquakes. The latter inevitably induces torsional demands, even in the case of full plan-wise symmetric structures, which add to bending, shear, and axial deformations. Unfortunately, current international building codes are not applicable for the design of nonplanar sections governed by warping torsion rather than circulatory torsion. This lack of information and guidance in building codes has resulted in a very limited number of structures being designed to account for warping stresses, even though the latter can be of a similar order of magnitude to bending stresses and, therefore, of major significance. A simple procedure is herein presented to estimate the ultimate warping moment and ultimate torque of nonplanar RC sections based on “warping-equivalent” ultimate bending moments from sectional analysis. A circular and bilinear bending moment-torque interaction relationship is proposed and compared to the existing, albeit limited, experimental and numerical results available in the literature.

For tall buildings, wind demand under extreme wind loads is so large that design based on conventional elastic behavior can be difficult. A practical solution is to permit inelastic behavior to introduce hysteretic damping and reduce design wind force. Therefore, the inelastic behavior of structures subject to wind loads should be thoroughly investigated. The presumption is that applications currently applied in inelastic seismic design can be employed in inelastic wind design of concrete buildings. In this research, behaviors of elastic, bilinear, and self-centering single-degree-of freedom systems under along-wind load were studied for various design wind speeds using nonlinear time-history analysis. Self centering systems—in particular, unbonded post-tensioned concrete systems—given their wide use and high potential and flexibility for self-centering behavior, were found to have smaller maximum displacement than bilinear systems, with differences being considerable at higher wind speeds. Results found highlight the role of post-yield stiffness in reduction of maximum displacement. Self-centering systems were also found to be highly influenced by reverse-yielding values. Systems with reverse yield strength equal to the standard deviation of the elastic force (approximately 20% of [mean + background + resonant components]) demonstrated minimum displacement. In addition, design parameters such as ductility, overstrength, and displacement factor are reported for inelastic design based on the concept of a response modification factor.

Shear walls are used to carry lateral loads and gravity loads in tall structures. Openings are an integral part of these walls for accommodating windows, doors, service ducts, and so on; these openings affect the entire behavior of the structures. This paper discusses experimental and numerical studies on high-performance concrete (HPC) and high-performance fiber-reinforced cement concrete (HPFRCC) slender shear walls with and without openings. Six shear wall specimens having a three-story height (one-fourth scaled down) were studied to understand the effects of the opening orientation and steel fibers on HPC shear walls. A significant reduction in strength and stiffness was observed in the specimens with openings (opening ratio 15.6%). The addition of steel fibers (volume fraction 0.5%) was more effective in the specimens with openings than the solid specimens. Models of the specimens developed in the finite element software ANSYS yielded results comparable to the experimental study. Two additional HPC and HPFRCC specimens were modeled to study the effect of different patterns of additional reinforcement around the openings. Replacement of vertical and horizontal reinforcing bars obstructed by the openings on the edges of the openings was most effective.

The design of reinforced concrete (RC) structures against fatigue failure due to shear loads is based on empirical approaches (refer to Eurocode 2). In particular, this unsatisfying status pertains to members without links such as bridge slabs or footings of wind energy plants. In terms of sustainability—for example, a longer service life of these structures—safe and exact calculation methods to determine their fatigue resistance are urgently needed. Therefore, the load-bearing behavior of RC elements without links under static and cyclic loads was studied theoretically, experimentally, and numerically at the Hamburg University of Technology (TUHH). Sixteen RC beams without shear reinforcement were tested under cyclic loads. The analysis of the time-consuming experimental investigations confirmed the EC2 approach to estimate the shear capacity of RC beams without links under fatigue loading, if the shear resistance under static loads is known from tests. The fib approach is too conservative. The specimens showed a high shear strength even after wide cracks had opened. Thus, the shear force is predominantly carried by the compression zone and not by crack friction.

Through accident or act of terrorism, structures may be subject to conditions that could lead to progressive collapse. Redistribution of loads following an imposed local damage to a structure depends on strength, continuity, redundancy, and deformation and energy dissipation capacities of the structure. For reinforced concrete frame structures, these characteristics depend on the seismic and wind design loads to a great extent. In this paper, using the response of multi-degree-of-freedom and equivalent single-degreeof-freedom systems, it is demonstrated that the vulnerability of frame structures against progressive collapse caused by man-made hazards depends heavily on their resistance to natural hazards. It is also shown that following the loss of a column and in spite of satisfying the current structural integrity requirements, premature beam bottom bar fracture can occur. Such bar fracture can be avoided if the minimum beam bottom continuous bars are set equal to the minimum flexural reinforcement.