Special issue: 2010 los angeles tall buildings structural design council—2010 magnitude 8·8 chile earthquakeMehrain, Michael; Lew, Marshall; Hart, Gary
doi: 10.1002/tal.682pmid: N/A
It is a pleasure to present the seventh annual issue developed by the Los Angeles Tall Buildings Structural Design Council. This two part issue is devoted to the Offshore Maule earthquake that shook Central Chile earlier this year. These two issues represent significant lessons learned from this earthquake. This earthquake is very significant as it presents a unique opportunity to study the effects of a true mega earthquake (with moment magnitude of 8·8) on modern tall buildings designed with contemporary building codes and constructed with modern construction methods. The building codes and construction methods are similar to those used in the USA so this event should be of interest to all structural engineers. This earthquake occurred on the South American subduction zone, which has uncanny similarities to other similar subduction zones around the world including the Cascadia subduction zone off the coast of the Pacific Northwest of the USA and Southern British Columbia, Canada; other subduction zones include those off of Alaska, Japan, Philippines and Indonesia. Thus, this earthquake gives us the first opportunity to develop an understanding of the behaviour of tall buildings to subduction zone events. Copyright © 2010 John Wiley & Sons, Ltd.
The significance of the 27 February 2010 offshore Maule, Chile earthquakeMehrain, Michael; Lew, Marshall; Hart, Gary
doi: 10.1002/tal.668pmid: N/A
The 27 February 2010 Offshore Maule, Chile earthquake is one of the most significant seismic and earthquake engineering events for many reasons but especially for the study of the dynamic behaviour of tall buildings. Because the earthquake occurred on a subduction zone where the convergence of the Nazca plate with the South American plate occurs, there are similarities to large areas of North America with similar conditions such as the Cascadia subduction zone extending from Northern California to British Columbia; major metropolitan areas that could be affected by the Cascadia subduction zone include Portland, OR, Seattle, WA and Vancouver, BC. The abundance of tall buildings in Chile, particularly in Santiago, Viña del Mar and Concepción, allow for significant case histories into the behaviour of tall buildings in Chile, a country that has similar design and construction practices to the USA, where there is also an abundance of tall buildings in major population areas. Copyright © 2010 John Wiley & Sons, Ltd.
Seismological and tectonic setting of the 27 February 2010 offshore Maule, Chile earthquakeMehrain, Michael; Lew, Marshall; Hart, Gary
doi: 10.1002/tal.677pmid: N/A
The magnitude 8·8 Offshore Maule, Chile earthquake is a significant event in seismology and earthquake engineering. The earthquake occurred on a convergent plate boundary (subduction zone) and affected a large area that a significant number of tall buildings designed to modern building codes. An understanding of the seismological and tectonic setting of this earthquake, together with understanding of the behaviour of structures, will further research and enhancements in seismic design in similar convergent plate boundary environments, such as the Cascadia subduction zone off the coast of the Pacific north‐west in the USA and Canada and other areas around the world. Copyright © 2010 John Wiley & Sons, Ltd.
Accelerographic measurements of the 27 February 2010 offshore Maule, Chile earthquakeMehrain, Michael; Lew, Marshall; Hart, Gary
doi: 10.1002/tal.673pmid: N/A
The mega earthquake of 27 February 2010, offshore Maule, Chile with moment magnitude of 8·8 is the fifth largest recorded earthquake in the world and, therefore, is considered to be a mega earthquake. This subduction interplate thrust earthquake occurred at the convergence of the Nazca (oceanic) plate with the South American continental plate. This type of earthquake affects the north‐western region of USA and Canada, as well as Alaska. Therefore, it is important to study the characteristics of the recorded accelerograms and their effects on the future behaviour of tall buildings in USA. Although the earthquake produced accelerographic records with very high ground motions in terms of peak ground accelerations and very long duration of ground shaking, the observed damage from this earthquake was more like the level of damage expected from a moment magnitude 8?0 rather than a moment magnitude of 8?8. This may be the result of asperities in the fault rupture surface. Copyright © 2010 John Wiley & Sons, Ltd.
Did the large coseismic displacement cause the global overturning collapse of the Alto Rio building during the 27 February 2010 Offshore Maule, Chile earthquake?Mehrain, Michael; Lew, Marshall; Hart, Gary
doi: 10.1002/tal.678pmid: N/A
A very large coseismic displacement (≈304 cm) was recorded at the city of Concepción during the moment magnitude (Mw) 8·8 Offshore Maule, Chile earthquake of 27 February 2010. The Alto Rio building, a 15‐storey reinforced concrete structure with two underground levels, experienced a global overturning collapse, resulting in the death of eight of its occupants. Ever since, a lingering question has preoccupied the minds of structural engineers and earth scientists: Did the large coseismic displacement cause the overturning collapse of this building? The answer based on the analyses provided in this paper is no. Copyright © 2010 John Wiley & Sons, Ltd.
Three‐dimensional wind load effects and wind‐induced dynamic responses of a tall building with X‐shapeMehrain, Michael; Lew, Marshall; Hart, Gary
doi: 10.1002/tal.514pmid: N/A
Three‐dimensional wind load effects on a tall building with X‐shape are investigated based on measured synchronous surface pressures in a wind tunnel. The mean and root‐mean‐square storey force coefficients in the three primary directions, i.e. along‐wind, crosswind and torsional wind, of the building are presented. Wind‐induced response analysis has been carried out in time domain by using the step‐by‐step numerical integration method, and the occupant comfort performance of the practical 42‐storey building is checked against the Chinese tall building design code. In the dynamic analysis, the buildings are modelled by a lumped mass system having three degrees of freedom at each floor level, i.e. two orthogonal translations and one rotation about a vertical axis. A new resultant displacement projection method is proposed to calculate the gust response factors (GRFs) along two orthogonal coordinate directions for design purpose. Not only can the calculated GRFs ensure the synchronization among the maximum resultant displacement and the maximum component displacements along X‐ and Y‐axes, but also are capable of taking crosswind effects into account. Copyright © 2009 John Wiley & Sons, Ltd.
Seismic performance of a 20‐story steel‐frame building in CanadaMehrain, Michael; Lew, Marshall; Hart, Gary
doi: 10.1002/tal.517pmid: N/A
In performance‐based seismic design of a structure, the inelastic deformation demand of structural members or system is the primary input, whereas in conventional design procedure the input is the equivalent static loads to represent seismic effects. The National Building Code of Canada (NBCC) 2005 requires that for irregular and buildings higher than 60 m, dynamic analysis must be conducted to calculate seismic design forces and deflection, while for other cases, equivalent static loads can be used for the design. In this paper, the performance of a 20‐story steel moment resisting steel frame building, designed for western part of Canada, has been presented. Simulated and actual (scaled) ground motion records are used to evaluate the dynamic response. While NBCC does not provide any performance‐based design method, various techniques for displacement‐based design have been explored here in the context of the 20‐story building. A wide range of variation amongst these methods in terms of their application and results was found. Amongst these methods the direct displacement‐based design method seems to be more suitable for carrying out the performance‐based design of a building. Copyright © 2009 John Wiley & Sons, Ltd.
Incremental dynamic analysis of high‐rise towersMehrain, Michael; Lew, Marshall; Hart, Gary
doi: 10.1002/tal.518pmid: N/A
The performance study of high‐rise towers has been attracting attention recently. Powerful analysis methods are used to assess local and global behaviour of tall structures. Incremental Dynamic Analysis (IDA) is one the most powerful methods for accurate estimation of seismic performance of structures. In this paper, IDA is applied on high‐rise towers, specifically Tehran telecommunication tower. Three different finite element models have been developed. The first model is a two‐dimensional fibre beam element model on which IDA is applied. The other two models are finely meshed three‐dimensional elastic and inelastic multi‐axial‐element‐based models, which are used to investigate the validity of the two‐dimensional model. Furthermore, the efficiency of different Intensity Measures and Engineering Demand Parameters is investigated. The results show that there is a good agreement between the results of two‐dimensional and three‐dimensional models in linear and nonlinear domains. It is also observed that Sa(T1) is more efficient than peak ground acceleration (PGA) as spectral acceleration is a structural specific intensity measure in comparison with, which is site‐specific. Copyright © 2009 John Wiley & Sons, Ltd.