Identification of key design parameters for earthquake resistance of reinforced concrete shell structures
Engineering Structures, 2017
Concrete roof shells have shown to be inherently able to sustain earthquakes, but the reasons for... more Concrete roof shells have shown to be inherently able to sustain earthquakes, but the reasons for this apparent seismic resistance have been subject to limited research. Concrete shells exhibit a high structural efficiency and thus can be constructed very thin. Because of their relative lightweight nature, the earthquake forces induced in a thin shell structure are relatively low. However, the shape of a shell structure is typically established so that it performs optimally under gravity loads, carrying the loads to the foundations mainly through membrane action over the shell surface. Unanticipated horizontal forces induced by earthquakes generate bending stresses in concrete shell structures, which could lead to structural damage. Through a parametric study of 8 cm thick, concrete roof shells with a square plan, the research presented in this paper demonstrates that small to mid-sized (span < 15 m) thin concrete roof shells can indeed be intrinsically earthquake resistant. They owe this resistance to their great geometric stiffness and low mass, which lead to high fundamental frequencies that are well above the driving frequencies of realistic seismic actions. Due to these characteristics the shells analyzed in this paper behave elastically under the earthquake excitation, without surpassing the maximum allowable concrete strength. For shallow shells it is observed that the vertical components of the earthquake vibrations, can induce larger stresses in the shell than the horizontal components. It is further demonstrated that by increasing the rise and curvature of larger shells (20 m by 20 m), their fundamental frequencies are increased and the damaging effect of the vertical earthquake vibration components mitigated.
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Papers by Tim Michiels
Concrete shell structures are generally believed to inherently perform well during earthquakes. They are characterized by a high mechanical efficiency and thus can be made very thin. Because of their lightweight nature, the induced earthquake forces are relatively low. However, shell structures are typically designed to perform optimally under gravity loads, carrying the loads to the foundations mainly through membrane action. The horizontal forces induced by earthquakes could thus create unanticipated bending stresses in the structure, which could lead to damage.
Thus, while several factors indicate that Candela’s shells might be intrinsically at a low risk for earthquake damage, the reasons for their good behavior are not yet understood. An in-depth examination of their perfor-mance under earthquake loading would enable professionals to develop a more effective conservation ap-proach, if necessary to protect them against future earthquakes. Perhaps more significantly, a better under-standing of why Candela’s concrete shells performed well during the 1985 earthquake could also inform the development of further earthquake-resistant shell structures.
This research presents a map which details the earthquake hazard of Candela’s structures in Mexico City based on their subsoil conditions as well as introduces an in-depth case study of the performance during the 1985 Mexico City earthquake of the 1953 Church of our Lady of the Miraculous Medal, one of Candela’s most emblematic structures.
Traditional techniques that enhance the stability of the building, such as wooden ring beams, wooden ties interconnecting parallel walls, corner keys and the addition of buttresses were found to be effective solutions since they employ compatible and low-cost materials such as earth and wood. When these techniques prove insufficient, minimally invasive measures such as introducing a plywood diaphragm, horizontal steel rods, a geomesh covered with mud rendering or a strapping system can be appropriate.
Concrete shell structures are generally believed to inherently perform well during earthquakes. They are characterized by a high mechanical efficiency and thus can be made very thin. Because of their lightweight nature, the induced earthquake forces are relatively low. However, shell structures are typically designed to perform optimally under gravity loads, carrying the loads to the foundations mainly through membrane action. The horizontal forces induced by earthquakes could thus create unanticipated bending stresses in the structure, which could lead to damage.
Thus, while several factors indicate that Candela’s shells might be intrinsically at a low risk for earthquake damage, the reasons for their good behavior are not yet understood. An in-depth examination of their perfor-mance under earthquake loading would enable professionals to develop a more effective conservation ap-proach, if necessary to protect them against future earthquakes. Perhaps more significantly, a better under-standing of why Candela’s concrete shells performed well during the 1985 earthquake could also inform the development of further earthquake-resistant shell structures.
This research presents a map which details the earthquake hazard of Candela’s structures in Mexico City based on their subsoil conditions as well as introduces an in-depth case study of the performance during the 1985 Mexico City earthquake of the 1953 Church of our Lady of the Miraculous Medal, one of Candela’s most emblematic structures.
Traditional techniques that enhance the stability of the building, such as wooden ring beams, wooden ties interconnecting parallel walls, corner keys and the addition of buttresses were found to be effective solutions since they employ compatible and low-cost materials such as earth and wood. When these techniques prove insufficient, minimally invasive measures such as introducing a plywood diaphragm, horizontal steel rods, a geomesh covered with mud rendering or a strapping system can be appropriate.