Probability-based LRFD for engineered wood construction

The newly developed load and resistance factor design (LRFD) specification for engineered wood construction in the United States uses probabilistic methods as the technical basis for selecting design strength requirements, load combinations and load factors. Special characteristics of wood and wood products as structural materials are considered. The strength of wood structural products depends on the rate of application and duration of the loads. LRFD criteria for the ultimate limit states account for this dependence by means of a time effect factor. The apparent increase in strength of wood structural systems comprised of several nominally identical and repetitively used members is taken into account with a system factor. Serviceability limit states of deflection and vibration are addressed with some general code guidelines and a nonmandatory commentary.     

Reliability analysis of prestressed concrete bridge girders: comparison of Eurocode, Spanish Norma IAP and AASHTO LRFD

The objective of this paper is to compare the reliability level of prestressed concrete bridge girders designed using three codes: Spanish Norma IAP-98 (1998), ENV 1991-3 Eurocode 1 (1994), and AASHTO LRFD (1998). Typical precast girders used in Spain are considered. Load and resistance parameters are treated as random variables. The statistical parameters are based on the available literature, test data and load surveys. Reliability indices are calculated by iterations. The results indicate that Eurocode is more conservative than the other two codes, and AASHTO LRFD is the most permissive code.     

The composite effect of steel fibres and stirrups on the shear behaviour of beams using self-consolidating concrete

Based on the investigation of the influence of steel fibre on the workability of fresh self-consolidating concrete (SCC), this paper presents the experimental results carried out on a series of simply supported SCC rectangular beams, using steel fiber reinforcement with and without stirrups, and subjected to four-point symmetrically placed vertical loads. The major test variables are the steel fibre content and stirrup ratios. The current study on the shear strength of conventional reinforced concrete (RC) beams verifies the shear strength of SCC beams with steel fibres. The investigation indicates that the shear strength significantly increases by increasing the fibre content; the addition of steel fibres in an adequate percentage can change the failure mode from a brittle shear collapse into a ductile flexural mechanism. The stirrups can be partially replaced by steel fibres. The combination of steel fibres and stirrups demonstrates a positive composite effect on the mechanical behaviour. The shear strength recorded experimentally is compared with the value obtained from the proposed formula, and the correlation is satisfactory.     

Full-scale long-term and ultimate experiments of simply-supported composite beams with steel deck

This paper presents the details of an experimental study carried out on two full-scale simply-supported composite steel-concrete beams to investigate their long-term behaviour and how this affects their ultimate response. The specimens were formed by a steel joist and a concrete slab with steel deck, and possessed identical spans and cross-sections. The ribs of the steel deck were orthogonal to the longitudinal axis of the steel joist, representing a secondary beam of a typical composite building flooring system. The beams were designed based on Australian guidelines with a degree of shear connection equal to 0.79. The samples were cast using unpropped construction. One specimen was kept unloaded for the entire duration of the tests. The second one was subjected to a sustained uniformly distributed load for about four months, after which it was loaded to failure. Particular attention was placed in this study on the occurrence of non-uniform shrinkage through the concrete thickness due to the presence of the profiled sheeting which prevented moisture egress to occur from the underside of the slab. Short- and long-term push-out tests were carried out to measure the response of the shear connectors over time. An analytical model was recommended to predict the long-term behaviour of composite beams with steel deck and its adequacy was validated against the reported experiments. For its simplicity, the proposed approach lends itself for design applications.