This paper presents a strategy to enhance the current provision for anti-buckling design of lateral ties. The resulting design method will restrict the buckling-induced reduction of average compressive stress of main bars to an allowable limit until the desired level of ductility is attained. First, a method to determine the maximum compressive strain likely to be experienced by the main bars is described. Based on an average compressive stress-strain relationship of reinforcing bars, evaluation of bar buckling parameter (a function of slenderness ratio and yield strength of the bar) required to restrict the loss of compressive stress at the maximum compressive strain to a tolerable limit is then explained. For a bar of known diameter and yield strength, the maximum allowable tie spacing can then be determined. Next, lateral stiffness required to restrain the buckling tendency of the main bars at the tie locations is expressed as a function of the geometrical and mechanical properties of the main bars. Similarly, the anti-buckling stiffness of the lateral ties is also derived as a function of the mechanical and geometrical properties of the lateral ties. Finally, a design framework to decide the spacing, amount and arrangement of lateral ties is established.
Paper P38: [Read]
Severe damage to six out of a total of 21 subway stations in the Kobe area during the 1995 Hyogoken-nanbu earthquake indicated a need for more attention to be given to the earthquake design of rectangular underground structures. This paper presents work undertaken to extend the present knowledge of the dynamic interaction of box-section structures with the surrounding soil, and a design method for predicting the earthquake loads on underground structures such as basement walls, tanks, subways, utility boxes, highway underpasses, and culverts.
Paper P39: [Read]
Michael Pender, Liam Wotherspoon, Jason Ingham and Athol Carr
We compare two approaches to the design of the foundations for low-rise reinforced concrete framed structures founded on discrete shallow footings. The underlying soil is stiff clay. The first approach considers the foundations separately from the structure, uses the equivalent static method to estimate foundation actions, and then proportions the foundations to have adequate bearing strength under these actions. The second considers an integrated model of the structure-foundation system. Computer modelling was undertaken using RUAUMOKO (Carr 2004), a nonlinear dynamic structural analysis program. The framed structures on shallow foundations, connected with tie beams (not considered to be part of the foundation), were analysed and the effects of structural yielding, nonlinear soil behaviour and foundation uplift were determined. Yielding and uplift characteristics of the foundations have been modelled by adapting available structural models in the software. The main conclusion from the paper is that the sophistication of the integrated computer model gives an enhanced understanding of the behaviour of the system that may lead to more economical foundation design.
Paper P40: [Read]
Kevin McManus, John Turner and Guillaume Charton
The use of inclined micropiles as reinforcement to prevent soil liquefaction in level ground has been investigated experimentally. Deposits of loose (Dr = 0.2 to 0.4), dry sand were prepared inside a large (2.0 m deep by 1.8 m long by 0.8 m wide) laminated box and subjected to shaking of different intensities on a one-dimensional shake table. For low intensity shaking (PGA up to 0.28 g) the cyclic shear strains were modest (up to 0.11 percent) and there was a modest settlement (0.31 percent). For higher intensity shaking, (PGA up to 0.40 g) there was a significant transformation in response with much greater cyclic shear strain (0.65 percent) and settlement (3.1 percent).
Paper P41: [Read]
Emily Reich and Andrew Charleson
This paper presents an investigation into potentially new seismic design strategies for buildings, derived from areas outside the customary scope of earthquake engineering. The research examines fields such as car design, molecular behaviour and animal structure. Six concepts were developed into systems that may be constructible. These are titled: Plate Springs, Inertia Valves, Tension Tendons, Structural Laminates, Structural Kinks and Complex Links. A summary of the proposed ideas in terms of anticipated seismic design attributes is presented as well as an evaluation of their originality, architectural value and future potential. At this stage, each of these proposals is only speculative. Their value lies in their existence as possibilities for future exploration, an indication perhaps of the future of seismic design.
Paper P42: [Read]
Mohamed El Gawady, P. Lestuzzi and M. Badoux
Recent earthquakes have shown repeatedly the vulnerability of Unreinforced Masonry (URM) buildings. Fibre Reinforced Plastic (FRP) composites can provide a retrofitting alternative for URM buildings. This paper presents results of dynamic tests investigating the in-plane behavior of URM walls retrofitted with FRP. Five half-scale walls were built, using half-scale brick clay units, and retrofitted on a single side. Two aspect ratios (1.4 and 0.7), two mortar types (M2.5, and M9), three composite materials (carbon, aramid, and glass FRP), three fibre structures (plates, loose fabric, and grids), and two retrofitting configurations (diagonal “X” and full surface shapes) were investigated. The test specimens were subjected to a series of synthetic earthquake motions on an uni-axial earthquake simulator. The retrofitting technique improved the lateral resistance of the URM walls by a factor of 2.9. However, the improvement in the lateral drift was less significant. Moreover, covering the full surface with composites worked better than the diagonal “X” retrofitting configuration.
Paper P43: [Read]