住宅工程裂缝和渗漏的成因及防治

住宅工程质量关系人民群众的切身利益,关系社会和谐。文章针对目前合肥地区住宅工程存在的主要质量通病——裂缝和渗漏的情况进行了统计分析,着重就渗漏防治措施从材料、设计、施工、监理等方面进行了较为详细的阐述。     

Roof Collapse, Magic Mart Store, Bolivar, Tennessee

This paper summarizes an investigation of the July 2, 1983, roof collapse of the Magic Mart store in Bolivar, Tennessee. The building was a onestory retail store of steel‐framed roof construction. The collapse occurred during a severe thunderstorm with intense rainfall. The investigation includes review of background information and eyewitness accounts of the collapse, review of design and construction documents, site investigation and sample collection, laboratory testing of samples of the collapse debris, and structural analyses. The initiating mode of failure was instability of one of the beam‐column connections of the roof framing, triggered by ponded roof water. The principal cause of the failure was inadequate buckling resistance of the unbraced and unstiffened beam‐column connections, due to major deviations in the construction from the design documents. Also contributing to the failure were ponding rain water caused by improper slope and drainage of the roof and the increased weight of roofing materials added during the 10‐year life of the building. The paper concludes with a summary of the results of a personal injury law suit resulting from the collapse, and with recommendations for improvement in design and construction practices based on the lessons learned from this failure.     

对执行器失效具有完整性的状态反馈律设计

本文考虑对执行器失效具有完整性的状态反馈律的设计问题。文中给出了这样的状态反馈律存在的一些充分条件和一个数值例子。     

Trace,failure and testing equivalences for communicating processes

A basic question in the theory of communicating processes is “When should two processes be considered equivalent?”. Attempts to answer this question have led to the concepts of observation equivalence, bisimulations, testing equivalence, failure equivalence, etc. The main point of this paper is to increase the understanding and motivation for two of these equivalences, namely failure and testing equivalences. The approach starts with the idea that the equivalence of processes should be reducible to the visible sequences of actions which a process performs in various contexts. This idea is implemented by a string-based semantic order for communicating processes where divergence is catastrophic. Under some assumptions about contexts, the resulting semantics is shown to be equivalent to theimproved failure semantics of Brookes and Roscoe⁽¹⁾ and also to themust testing-semantics of Hennessy and DeNicola.^(2–4) This characterization gives independent support for the appropriateness of failures and testing.     

Collapse of Suspended Portland Cement Plaster Stucco Soffit

The collapse of a suspended soffit consisting of portland cement plaster stucco on metal lath was investigated to determine the probable cause of collapse after over 30 years of service. Soffits of this type are often constructed with minimal, if any, details provided by the project architect or engineer. Without design guidance, the builder usually relies on typical industry practices and prior experience to construct these soffits. While experience may result in a safe installation in many instances, long-term performance without distress is no guarantee that no defects exist.     

A simple technique for automated performance testing of piezoelectric micro-motors by transient motion analysis

An automated method of testing a 5 mm diameter flextensional ultrasonic motor has been assembled using off-the-shelf components, which derives performance measurements from the transient start up and stopping behaviour of the motor using a non-contact position encoder. The method gives full performance characteristics in less than a second and it is scaleable for use with other sizes and other types of motor. Furthermore, it provides a relatively simple technique for non-contact measurements of position, angle or velocity that can be rapidly cycled as part of a development programme.

The method has shown sufficient sensitivity, using basic components, to measure torque in the range 10–200 μN m and speed in the range from 0 to over 2000 rpm. The torque and speed ranges are only dependant on the sensitivity of encoder instrumentation, inertial load on the motor and data acquisition. This system is believed to be a significant improvement over previously reported work that has detailed friction brake or manual ‘one-off’ systems and the test format has greater applicability for micro-motors that are used for their positioning capabilities.     

Analysis of long flow lines with quality and operational failures

This paper presents approximation methods for the performance analysis of long manufacturing lines, i.e. lines with more than two machines and one buffer, that have both quality and operational failures. We describe three different versions of long flow lines that differ in the locations of the inspection stations and in the sets of machines that each inspection station monitors. We explain a transformation method that approximates long manufacturing lines that have quality and operational failures with long lines that only have operational failures. Such lines can be evaluated by decomposition methods. We introduce other approximations to quantify the effects of the separation of inspections from operations. Comparison with simulation shows that the solution methods provide reliable performance estimates.     

Analysis of Causes of Falsework Failures in Concrete Structures

A study of 85 major falsework collapses of bridges and buildings in the past 23 yrs has documented the types of collapsed falseworks and failed permanent structures, the construction stages at the time of collapse, and the causes of failures. Three causes of failure were identified: triggering; enabling; and procedural causes. Most failures occurred because of the interaction of the triggering and enabling events that were, in many cases, produced by inadequacies in the procedural methods. Impact forces resulting from concreting operations have repeatedly triggered falsework failures that were enabled by deficiencies in the falsework bracings, components, connections, foundations, and design. Inadequate review of falsework design and monitoring procedures were frequent problems that facilitated the occurrernce of these events. The findings emphasize the importance of proper delineation of responsibility of each party in the building process in order to reduce falsework failures in the future.     

Analysis of sequential failures for assessment of reliability and safety of manufacturing systems

Assessment of reliability and safety of a manufacturing system with sequential failures is an important issue in industry, since the reliability and safety of the system depend not only on all failed states of system components, but also on the sequence of occurrences of those failures. Methods that are currently available in sequential failure analysis always start with given sequences of the failures in the system, which is not the case in real life situations; therefore, the sequences of the failures should be identified and the probability of their occurrence should be determined. In this paper, we represent a methodology that can be used for identifying the failure sequences and assessing the probability of their occurrence in a manufacturing system. The method employs Petri net modeling and reachability trees constructed based on the Petri nets. The methodology is demonstrated on an example of an automated machining and assembly system.