Integrated health monitoring for reinforced concrete beams: an experimental study

Civil infrastructures begin to deteriorate once they are built and used. Detecting the damages in a structure to maintain its safety is a topic that has received considerable attention in the literature in recent years. In vibration-based methods, the first few modes are used to assess the locations and the amount of damage. However, a small number of the global modes are not sufficient to reliably detect minor damage in the structure. Also, a common limitation of these techniques is that they require a high-fidelity model of the structure to start with, which is usually not available. Recently, guided waves (GW) have been found as an effective and efficient way to detect incipient damages due to its capacity of relatively long propagation range as well as its flexibility in selecting sensitive mode-frequency combinations. In this paper, an integrated structural health monitoring test scheme is developed to detect damages in reinforced concrete (RC) beams. Each beam is loaded at the middle span progressively to damage. During each loading step, acoustic emission (AE) method is used as a passive monitoring method to catch the AE signals caused by the crack opening and propagation. After each loading step, vibration tests and guided wave tests are conducted as a combined active monitoring measure. The modal parameters and wave propagation results are used to derive the damage information. Experimental results show that the integrated method is efficient to detect incipient damages in RC structures.

Embodied energy in buildings : wood versus concrete - reply to Börjesson and Gustavsson

We analyse the wood and concrete designs of the Wälludden building described by Börjesson et al. (Energy Policy 28 (2000) 575) in terms of their embodied energy, employing an environmentally extended input–output framework in a tiered hybrid life-cycle assessment, and in a structural path analysis. We illustrate the complexity of the inter-industry supply chains underlying the upstream energy requirements for the building options, and demonstrate that higher-order inputs are difficult to capture in a conventional process analysis. Our calculations show that Börjesson and Gustavsson's estimates of energy requirements and greenhouse gas emissions are underestimated by a factor of about 2, and that corresponding greenhouse gas balances are positive at about 30 t C-eq. Nevertheless, Börjesson and Gustavsson's general result—the concrete-framed building causing higher emissions—still holds.

On the acoustic performance of a precast panel system made from environmentally sustainable concrete : application in sports hall buildings

The use of green building materials and products promotes conservation of non-renewable resources and help reduce associated environmental impacts. This article reports the acoustical performance of a precast panel system made largely from concrete waste material. Two major applications for such panels that are being investigated currently include walls and claddings to industrial and commercial buildings and sound barriers for urban freeways. In this study, the application of the concrete panels for optimizing reverberation time (RT) in sports halls is tested using numerical simulations. As an innovative approach, additional layers are added to the precast panels to improve their appearance. The absorption coefficients of the concrete panel improved significantly with the architectural finish. The material can be tuned according to the required peak frequency. The architectural finish helped reduce the RT for frequencies above 500 Hz. Its application to different types of ceilings revealed that the RT of curved ceiling reduced up to 40% compared to flat and hybrid ceiling. A comparison of wall and ceiling modifications in small, medium and large sports halls showed that medium-sized halls have better acoustical performance compared with small and large halls with ceiling as well as wall treatment.