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CONTENTS
Volume 3, Number 4, August 2003
 

Abstract
This paper deals with the formulation and development of fracture criteria for high-strength structural members containing surface damage in the form of notches (i.e., blunt defects). The important role of the yield strength of the material and its strain hardening capacity (evaluated by means of the constitutivernlaw or stress-strain curve) is analysed in depth by considering the fracture performance of notched samples taken from high-strength steels with different levels of cold drawing (the most heavily drawn steel being commercial prestressing steel used in prestressed concrete). The final aim of the paper is to establish fracturebased design criteria for structural members made of steels with distinct yield strength and containing very different kinds of notch-shape surface damage.

Key Words
fracture criterion; high-strength steel; cold drawn wires; notched structural members; structural engineering.

Address
Department of Materials Engineering, University of Salamanca, E. P. S., Campus Viriato, Avda. Requejo 33, 49022 Zamora, Spain

Abstract
This paper reports on the development of a new composite slab system that uses a large- lipped steel channel and reinforced concrete. The advantages of this new system are that it serves as both a structural unit and an unsupported form and it has a secondary structural barrier function. A concrete pouring test wasrncarried out for the large-lipped steel channel. Full-scale tests were carried out to assess the flexural strengthdeformation characteristics and structural mechanics of the composite slab. The barrier mechanics of the steel channel concrete element (referred to as the SC subunit) of the composite slab are examined. The test resultsrnindicate that the new composite slab has excellent strength, ductility haracteristics, and a structural barrier function in its SC subunit that is highly effective against severe loading.

Key Words
large-lipped steel channel; composite slab; flexural strength; structural barrier function; structural index.

Address
Department of Architecture, Maebashi Institute of Technology, 460-1, Kamisadori-machi, Maebashi-ci, Gunma Pref., 371-0816, Japan

Abstract
Truss members built-up with double angles back-to-back have monosymmetric cross-section and twisting always accompanies flexion upon the onset of buckling about the axis of symmetry. Approximate formulae for calculating the buckling capacity are presented in this paper for routine design purpose. For a member susceptible only to flexural buckling, its optimal cross-section should consist ofrnslender plate elements so as to get larger radius of gyration. But, occurrence of twisting changes the situation owing to the weakness of thin plates in resisting torsion. Criteria for limiting the leg slenderness are discussed herein. Truss web members in compression are usually considered as hinged at both ends for out-of-plane buckling. In case one (or both) end of member is not supported laterally by bracing member, its adjoining members have to provide an elastic support of adequate stiffness in order not to underdesign the member. Thernstiffness provided by either compression or tension chords in different cases is analyzed, and the effect of initial crookedness of compression chord is taken into account. Formulae are presented to compute the required stiffness of chord member and to determine the effective length factor for inadequately constrainedrncompressive diagonals.

Key Words
truss; double-angle section; flexural-torsional buckling; width-thickness ratio; elastic support; lateral stiffness; bracing; effective length.

Address
School of Civil Engineering, Xi

Abstract
The low boundary of load carrying capacity of the elastic-plastic spatial grid structures depend on numerous values and their variability assumed in designing process. Analysed influence all this values in searching for optimal variant of the structure lead to too great problem even taking into consideration actualrncomputational power we have in disposal. Therefore one can take only a few values which have greatest influence on the optimal choice. In optimal analysis of the elastic-plastic spatial grid structures the previously proposed method with subsequent modification (Karczewski 1980), (Karczewski, Barszcz and Donten 1996), (Karczewski and Donten 2001) as well as computer program which was worked out by Donten K. to make possible practical utilisation this method was employed. The paper deal with evaluation of influence dimensions of particular values for choice of optimal variant of the structure. One among this values isrndistribution of the struts in the structure.

Key Words
spatial grid structures; plastic analysis; optimisation; decisive variable; objective function; distribution of the strut.

Address
The Building Structures Institute, Warsaw University of Technology, Ul. Armii Ludowej 16, 00-673 Warsaw, Poland

Abstract
A series of tests was conducted to study the behaviour of steel-composite sandwich beams under low velocity hard impact. Damage characteristic and performance of sandwich beams with different spacing of shear connector were evaluated under impact loading. Thin steel plates were used as top and bottom skins of the sandwich beams and plain concrete was used as the core material. Shear connectors were provided by welding of angle sections on steel plates. The sandwich beams were impacted at their midpoint by a hemispherical nose shaped projectile dropped from various heights. Strains on steel plates were measured to study the effects of impact velocity or impact momentum on the performance of sandwich beams. Spacing of shear connectors is found to have significant effects on the impact response of the beams.

Key Words
experimental research; low velocity impact; sandwich composite beam; shear connector; strain time response.

Address
Department of Civil Engineering, National University of Singapore, BLK E1A, #07-03, 1 Engineering Drive 2, Singapore 117576


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