This paper addresses the problem of assessing the seismic resistance of brick masonry walls subject to out‐of‐plane bending. A simplified linearized displacement‐based procedure is presented along with recommendations for the selection of an appropriate substitute structure in order to provide the most representative analytical results. A trilinear relationship is used to characterize the real nonlinear force–displacement relationship for unreinforced brick masonry walls. Predictions of the magnitude of support motion required to cause flexural failure of masonry walls using the linearized displacement‐based procedure and quasi‐static analysis procedures are compared with the results of experiments and non‐linear time‐history analyses. The displacement‐based procedure is shown to give significantly better predictions than the force‐based method. Copyright © 2002 John Wiley & Sons, Ltd.

This paper presents the results of static and dynamic tests on unreinforced brick masonry wall panels subject to out-of-plane loading. Fourteen wall panels were tested. The test program included static, free-vibration, and dynamic tests using harmonic support, impulse support, and earthquake support motion. The experimental results indicate that displacement, rather than inertia force amplitude, determines whether an unreinforced masonry wall will collapse during inertial ͑seismic͒ loading. An empirical force-displacement relationship is proposed that can be used for a substitute structure in a displacement-based method of analysis.

SUMMARYThis paper addresses the problem of assessing the seismic resistance of brick masonry walls subject to out-of-plane bending. A simpliÿed linearized displacement-based procedure is presented along with recommendations for the selection of an appropriate substitute structure in order to provide the most representative analytical results. A trilinear relationship is used to characterize the real nonlinear forcedisplacement relationship for unreinforced brick masonry walls. Predictions of the magnitude of support motion required to cause exural failure of masonry walls using the linearized displacement-based procedure and quasi-static analysis procedures are compared with the results of experiments and nonlinear time-history analyses. The displacement-based procedure is shown to give signiÿcantly better predictions than the force-based method.

Two areas of shale diapirism in a deltaic setting were examined using 3D seismic data from offshore Brunei to determine the origin, evolution and geometry of shale diapirs. The study areas cover parts of the Egret and Ampa fields within the Baram Delta province. The Ampa diapir consists of a small bulge of the mobile Setap shale around which lies a zone of chaotically disrupted country-rock reflections. At the crest of this chaotic zone, vertical, cylindrical shale pipes arise that end in a wider head. The diapir heads wear halos of high amplitude reflections, probably due to the presence of methane gas. The Egret data show the same features, except that the bulge of the source layer is not detected due to low reflectivity and chaotic reflections at the base of the overburden. The bulging of the Setap shale on the Ampa data is interpreted as modified reactive diapirism in response to differential loading. The initial reactive diapir shape was modified by lateral or oblique upward migration of fluidized shales into the hanging wall of the fault controlling the reactive diapir. This probably occurred as a network of dykes and sills. The presence of some preserved bedding is indicated by weak but coherent reflectivity from the area initially defined as chaotic shale. The spreading of overpressure and the injection of shale into the overburden is thought to be a late phenomenon, possibly Late Pliocene or Early Pleistocene and the mobility of the shale is attributed to overpressure increase due to gas generation within the Setap shale and maybe the lower part of the overburden. Gas migration, perhaps ahead of the diapir intrusion, probably facilitated the mud injection. The Ampa and Egret diapirs formed in two diapiric phases, an early reactive diapirism and a later active diapirism. But the phases have little in common; they are seperated by about 9 million years of inactivity and differ in process and probably differ in degree of overpressure, in overpressure generating mechanism, and in properties of the diapiric mud.

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