It is my pleasure to bring you the penultimate editorial of 2022 of your journal Structures and Buildings. In this issue, our readership will find five research articles, three of which focus on different aspects of seismic forces on structures. These three interesting contributions come from Iran, a country which has experienced the destructive effects of earthquakes in the past. The other two articles are devoted to concrete-filled steel tube (CFST) columns and damage detection in bridges. I am confident that you will find these scientific contributions both interesting and useful.
The seismic analysis of in-plan asymmetric buildings is usually performed carrying out non-linear response history analysis (NRHA) in three dimensions, which is a complex and time-consuming task. This is even more complex if the flexibility of the foundation needs to be considered in the analysis. To bypass these drawbacks, the first article in this issue (Teymoorian and Halabian, 2022) proposes an approximate method for the non-linear analysis of three-dimensional (3D) asymmetric buildings on flexible foundations subjected to bi-directional ground motions. The authors first introduce an uncoupled modal response history analysis (UMRHA) that is used to study the response of asymmetric structures supported on an elastic half-space medium. Next, the authors present an innovative five-degrees-of-freedom (5DoF) modal stick that extends the applicability of the above-mentioned method to account for non-linear deformations of the superstructure. Based on two case study buildings, Teymoorian and Halabian (2022) show that the approximate method (which is less complex and computationally demanding) gives similar results to those given by a more rigorous NRHA.
In the second contribution of this issue, Shakeri et al. (2022) study the behaviour of steel moment-resisting frames (MRFs) subjected to sequential earthquakes (i.e., a foreshock followed by a mainshock and an aftershock). Numerical models of special and intermediate MRFs of four and eight floors were subjected to incremental dynamic analyses. The authors found that, in 60% to 80% of the analyses using sequential earthquakes, both special and intermediate MRF models failed due to the aftershock event. Moreover, intermediate MRFs designed for a life safety performance level can experience a higher risk of collapse when subjected to sequential earthquakes.
Our readership interested in reinforced concrete (RC) walls and high-rise buildings are invited to read the article by Beiraghi and Kheyroddin (2022). The authors start their article by providing a very informative and suitable insight into four different approaches to design RC core wall buildings: single plastic hinge (SPH) at the wall's base, dual plastic hinge (DPH), triple plastic hinge (TPH) and extended plastic hinge (EPH) approaches. Thirty-, 40- and 50-storey buildings were designed adopting the four design approaches, and subsequently modelled in Perform3D software. Non-linear time history analyses (NLTHA) using far-field ground motions were performed on such buildings. It was found that, for a maximum credible earthquake and a DPH approach, the most reasonable location of the second plastic hinge is the building's mid-height, or 0.5H. Likewise, the best locations for the second and third plastic hinges in the TPH approach were 0.3H and 0.64H. The TPH approach was found to be the most convenient to design RC core walls as plastic hinges form at predetermined levels, and thus other parts of the wall would not need special reinforcement detailing for plastic hinging.
CFST columns are extensively used in the construction of multi-storey buildings. The fourth article in this issue investigates experimentally the feasibility of using a bolted-flange connection in CFST columns subjected to axial compression (Shehab and Ekmekyapar, 2022). The proposed column–column connection (located at the columns’ mid-height) aims to ease assembly and disassembly of CFST columns. The experimental results demonstrate that the behaviour of CFST columns with a bolted-flange connection is similar to that of CFST columns with no connection. The use of vertical stiffeners at the connection increased the toughness of the columns by up to 22%. The authors also conclude that the Eurocode 3 (BSI, 2005) design criteria (for the bolted-flange connection of a hollow circular steel tube subjected to tension) can be used for a bolted-flange CFST connection subjected to compression, but with considering some minor distance requirements. Readers working in the field of composite construction will find this article particularly stimulating.
The final article in this issue is an excellent example of how statistical methods and powerful computers can help us solve challenging issues in civil engineering. The article by Soo Lon Wah et al. (2022) presents a novel method to detect damage in existing structures. The method combines a principal component analysis, a Gaussian mixture model and outlier analysis. In this article, the method is applied to a database of natural frequencies and corresponding temperature measurements from the (undamaged) Z24 Bridge in Switzerland. This bridge was selected as representative of a typical structure subjected to bilinear effects from changing temperature conditions. The results show that the proposed method can successfully identify undamaged and damaged cases with success rates of 99% and 97.2%, respectively. Readers working in the fields of structural health monitoring will find this contribution particularly useful.
As usual, the editorial team of the journal is open to receive discussions on the above articles, as well as any comments or suggestions you may have.
