Moussa Leblouba

Static lateral stiffness of wire rope isolators

ABSTRACT This paper presents an analytical model for the static lateral stiffness of Wire Rope Isolators (WRI). The wire rope isolator, which is a passive isolation device, has been widely adopted as a shock and vibration isolation for many types of equipment and lightweight structures. The major advantage of the WRI is its ability to provide isolation in all three planes and in any orientation. The WRI in the lateral roll mode, is required to possess the required lateral stiffness to support and isolate the equipment effectively. The static lateral stiffness of WRI depends mainly on the geometrical characteristics and wire rope properties. The model developed in this paper is validated experimentally using a series of monotonic loading tests. The flexural rigidity of the wire ropes, which is required in the model, was determined from the transverse bending test on several wire rope cables. It was observed that the lateral stiffness is significantly influenced by the wire rope diameter and height of the isolator. The proposed analytical model can be used for the evaluation of lateral stiffness and in the preliminary design of the WRI.

Geotechnical Mapping of Seismic Risk for Sharjah City, United Arab Emirates

Seismic hazard and geotechnical microzonation maps of urban communities make it conceivable to describe potential seismic zones that should be considered when planning new structures or retrofitting existing ones. This study looked at a local site-specific ground response analysis, which is an important step in estimating the effects of earthquakes. The soil data from 200 boreholes up to 30 m depth were collected and analyzed using SHAKE2000 and NovoLiq in order to develop local site amplification and liquefaction potential maps for the city of Sharjah. In addition, Geographical Information System (GIS) was utilized to create amplification and liquefaction potentials maps at different areas in Sharjah. These maps show zones of high vulnerability earthquake risk used for earthquake-resistant design of structures. The city of Sharjah was divided into areas, according to the amplification factor, which ranged from 1.44 to 1.83. A high amplification factor was found near the central region of the city, while the rest of the city lies in low amplification potential and relatively low seismic risk. Finally, liquefaction risk of Sharjah estimated and expressed in terms of safety factor. The low values of the safety factors against liquefaction were found in the north, northeastern, and southeastern portions of the city. Higher values were found in central and toward south central parts of the studied area. In these parts, the higher safety factor indicates low liquefaction potential of the soil and relatively low seismic risk.

Practical Soil-Shallow Foundation Model for Nonlinear Structural Analysis

Soil-shallow foundation interaction models that are incorporated into most structural analysis programs generally lack accuracy and efficiency or neglect some aspects of foundation behavior. For instance, soil-shallow foundation systems have been observed to show both small and large loops under increasing amplitude load reversals. This paper presents a practical macroelement model for soil-shallow foundation system and its stability under simultaneous horizontal and vertical loads. The model comprises three spring elements: nonlinear horizontal, nonlinear rotational, and linear vertical springs. The proposed macroelement model was verified using experimental test results from large-scale model foundations subjected to small and large cyclic loading cases.

Elliptical Leaf Spring Shock and Vibration Mounts with Enhanced Damping and Energy Dissipation Capabilities Using Lead Spring

We present an enhancement to the existing elliptical leaf spring (ELS) for improved damping and energy dissipation capabilities. The ELS consists of a high tensile stainless steel elliptical leaf spring with polymer or rubber compound. This device is conceived as a shock and vibration isolator for equipment and lightweight structures. The enhancement to the ELS consists of a lead spring plugged vertically between the leaves (referred to as lead-rubber elliptical leaf spring (LRELS)). The lead is shown to produce hysteretic damping under plastic deformations. The LRELS isolator is shown to exhibit nonlinear hysteretic behavior. In both horizontal directions, the LRELS showed symmetrical rate independent behavior but undergoes stiffening behavior under large displacements. However, in the vertical direction, the LRELS behavior is asymmetric, exhibiting softening behavior in compression and stiffening behavior in tension. Mathematical models based on the Bouc-Wen model, describing the hysteretic behavior of the proposed isolator, are developed and numerically calibrated using a series of finite element analyses. The LRELS is found to be effective in the in-plane and vertical directions. The improved damping and energy dissipation of the LRELS is provided from the hysteretic damping of the lead spring.