Case Studies in Structural Engineering最新文献

This paper presents a comparative experimental study on the physical, chemical and mechanical properties of indirectly formed hot-formed, hot-finished and cold-formed structural steel rectangular hollow sections. Characteristic geometrical parameters and chemical compositions are examined to investigate the physical and chemical differences. Tensile test and charpy V-notch impact test are employed to evaluate the difference in strength, ductility and toughness. Further, the residual stress distributions in both transverse and longitudinal directions are measured using the sectioning method and hole-drilling technique. It is found out that although the geometrical parameters and chemical composition of the tested hollow sections are similar, the mechanical properties are significantly different, especially for strength, ductility and residual stress distribution. While the hot-finished and hot-formed sections are often treated equally in design, their mechanical properties and residual stresses distribution are actually different.

A primary school in Rotonda was monitored during an on-going seismic sequence in the Pollino area, Southern Italy. The Reinforced Concrete (RC) building is a typical three story building with a concrete frame, bearing pre-cast slab flooring, concrete block internal walls and pre-cast external infill slabs. The monitoring began in September 2011 with a single station on top of the building, and after the M_L = 5 mainshock occurred in October 2012 a network was completed with accelerometers on each floor and real-time streaming data was transmitted to the Istituto Nazionale di Oceanografia e Geofisica Sperimentale (Udine-Northern Italy). The school suffered no visible damage during the sequence. The real-time monitoring of the Rotonda school proved to be important for two reasons: (1) the large range of magnitudes and recorded peak accelerations allowed the study of the non-stationary frequency response; (2) the results also show how a simple, real-time monitoring system using cost-effective accelerometers could be used as a tool to provide information on the damage state and usability of the school.

The NMIT Arts & Media Building in Nelson, New Zealand is the first in a new generation of multi-storey timber structures. It employs a number of innovative timber technologies including an advanced damage avoidance earthquake design that is a world first for a timber building. Aurecon structural engineers are the first to use this revolutionary Pres-Lam technology developed at the University of Canterbury.

This technology marks a fundamental change in design philosophy. Conventional seismic design of multi-storey structures typically depends on member ductility and the acceptance of a certain amount of damage to beams, columns or walls. The NMIT seismic system relies on pairs of coupled timber shear walls that incorporate high strength steel tendons post-tensioned through a central duct. The walls are centrally fixed allowing them to rock during a seismic event. A series of U-shaped steel plates placed between the walls form a coupling mechanism, and act as dissipaters to absorb seismic energy. The design allows the primary structure to remain essentially undamaged in a major earthquake while readily replaceable connections act as plastic fuses.

With a key focus on sustainability the extensive use of timber and engineered-wood products such as laminated veneer lumber (LVL) makes use of a local natural resource, all grown and manufactured within an 80 km radius of Nelson.

This IstructE award winning project demonstrates that there are now cost effective, sustainable and innovative solutions for multi-storey timber buildings with potential applications for building owners in seismic areas around the world.

This paper presents a study about the spatial variability effects of ground motions on the dynamic behavior of a suspension bridge by a random vibration based spectral analysis approach and two response spectrum methods. Bosphorus Suspension Bridge built in Turkey and connects Europe to Asia in Istanbul is selected as a numerical example. The spatial variability of ground motions between the support points is taken into account with a coherency function that characterizes the incoherence, wave-passage and site-response effects. Power spectral density function and response spectrum values used in random vibration analyses are determined depending on the recordings of August 17, 1999, Kocaeli, Turkey earthquake. From the results, it can be observed that the structural responses for each random vibration analysis depend largely on the intensity and frequency contents of power spectral density functions.

The use of fibre reinforced polymer (FRP) bridge decks has attracted increasing interest as a competitive alternative to traditional decking solutions. Even though the use of FRP decks started in the early 1990s, the uptake of these decks has been slow in bridge construction and there remains a need for research in diverse technical areas to promote the widespread use of these decks. One such area is the detailing and design of deck panel level connections which enable rapid on-site assembly. The development of connections in FRP decks is a somewhat complex process, which should take account of not only the structural performance and durability of the joint but also the ease of application and the tolerances this necessitates. It should therefore be regarded as a process in which the bridge owner, the designer, the manufacturer and the contractor are all involved. This process has been applied in the development of a novel joint configuration for panel level connections presented in this paper. The collaboration between the bridge owner, designer, manufacturer and contractor led to the development of a connection concept, in which expectations originating from the views of all parties were included. In this way, a concept focusing on meeting the requirements of all bodies was designed.

Plastics are increasingly combined with renewable fibers to form materials such as wood-plastic composites (WPCs). These bio-based materials have gained the interest of the resource-intensive building industry and are currently used mainly for decking and cladding. Despite their environmental friendliness, WPC façades are still underrepresented in the market. This fact raises the question of whether WPC cladding is currently well positioned in the market and whether its attributes are advertised in a way that makes it stand out in a material selection process. A review of standards and codes relevant to façade design was carried out in this study, which allowed the identification of 21 product attributes as potential deciding factors in cladding product selection. Subsequently, the most promising attributes were used to assess commercially available plastics-based cladding products. By using multi-criteria decision making (MCDM) it was found that WPC cladding is still far behind other cladding products with respect to standard compliance but has specific properties which support product optimization. MCDM can be used by WPC cladding manufacturers for strategic product development and by façade designers for material selection processes.

In the practical design of nuclear building structures subjected to an aircraft crash, the structures are required to prevent scabbing and perforation. NEI 07-13 provided the formulas to predict the minimum reinforced concrete (RC) wall thickness to prevent the local damage caused by aircraft engine impact. However, these formulas may not be suitable for predicting the thickness of the ultra-high performance fiber reinforced concrete (UHPFRC) wall. In this study, the local damage of a UHPFRC wall caused by the impact of aircraft engine missile is investigated using a finite element program LS-DYNA. The structural components of the UHPFRC panel, aircraft engine model, and their contacts are fully modeled. The analysis results are verified with the test results. A parametric study with varying panel thickness, fiber type and content, and impact velocity is performed to investigate the local damage of the UHPFRC panel. Based on a comparison with the given formulas, the modified equations of Chang and Degen are proposed to predict the minimum wall thickness to prevent scabbing and perforation in the case in which the UHPFRC structure is used.

Bio-based materials, such as wood–plastic composites (WPC), have gained the interest of the resource-intensive building industry. Presently, this novel composite is being used in decking and cladding. The structural design of façades made from WPC compounds, however, has been difficult in the past due to a lack of design principles and experience.

In this case study a design concept is developed, which combines material attributes describing the strength loss of the material due to different weathering processes on façades. Although this approach is widely used for approvals of cladding kits in Central Europe, it has not yet been used for WPCs. This paper is unique because for the first time research findings taken from a literature review on WPC attributes are used to obtain a realistic WPC design value for engineered façades. Simulations of WPC aging in three main categories predicted a strength loss of approximately 50% compared to the virgin material. Nevertheless, a WPC material design value which includes the effects of material aging is still useful for a façade planner’s practical work in view of the mandatory codes and standards in this field.

This paper presents a methodology for probabilistic assessment of masonry vaults bearing capacity with the consideration of existing defects. A comprehensive methodology and software package have been developed and adapted to inspection requirements. First, the mechanical analysis model is explained and validated by showing a good compromise between computation time and accuracy. This compromise is required when probabilistic approach is considered, as it requires a large number of mechanical analysis runs. To model the defect, an inspection case is simulated by considering a segmental vault. As the inspection data is often insufficient, the defect position and size are considered to be unknown. As the NDT results could not provide useful and reliable information, it is therefore decided to take samples with the obligation to minimize as much as possible their number. In this case the main difficulty is to know on which segment the coring would be mostly efficient. To find out, all possible positions are studied with the consideration of one single core. Using probabilistic approaches, the distribution function of the critical load has been determined for each segment. The results allow to identify the best segment for vault inspection.

This paper presents a formulation for the design of reinforced concrete flexural members. The formulation yields exactly the same results as the current American Concrete Institute (ACI) design approach but it is based entirely on the concept of reinforcement ratios. This is in contrast to the current ACI approach which relies on strain limits [1]. A formulation based on reinforcement ratios is simpler and more intuitive and therefore has important pedagogical advantages. The formulation presented here can be thought of as an attempt to reconcile the new approach to design introduced by the ACI code in 2002, with the traditional approach to design that was in use from 1963 to 2002. The traditional approach to design of reinforced concrete sections uses the concept of reinforcement ratios. The new ACI approach, referred to here as the unified design method (UDM), requires consideration of rather cumbersome strain limits and/or geometric strain relationships. In this paper, it is shown that the UDM approach can be formulated much in the same way as the traditional approach, as long as a series of formulas involving reinforcement ratios are introduced. These formulas are presented in this paper. Many of them are well known, but some are new. In particular, a new formula for the compression-controlled reinforcement ratio limit, and a new direct procedure for the design of transition-zone sections are presented. The formulation presented in this paper should prove useful both for the instructor in the classroom, and for the practicing structural engineer. Derivation details for many of the formulas in the paper are given and several numerical examples to illustrate their use are provided at the end.