Lyle P. Carden

The New ASCE Tsunami Design Standard Applied to Mitigate Tohoku Tsunami Building Structural Failure Mechanisms

The last decade of destructive tsunamis in the Indian Ocean, and Pacific Ocean near Samoa, Chile and Japan have demonstrated the increasing vulnerability of coastal populations and built infrastructure to this hazard. In the United States, a new chapter has been developed for the ASCE 7 loading standard to design important buildings and other structures for tsunami loads and their effects. The application of the proposed ASCE 7 tsunami design provisions is demonstrated in the context of reinforced concrete and structural steel buildings analyzed for tsunami loads from the March 2011 Tohoku Tsunami, where the details of their structural performance were surveyed. Based on the case studies, the Energy Grade Line method of analysis is shown to be a reliable and generally conservative method to determine flow depth and velocity at a site based on a known maximum runup, with a modification to the Froude number coefficient for the bore condition. The load equations and conditions of ASCE 7 resulted in reasonable and conservative estimates of forces on components for hydrostatic buoyancy, lateral hydrostatic and hydrodynamic forces. Mid- to high-rise buildings, which are optimal for tsunami refuge, can be economically designed for life safety or better performance for large tsunamis with local strengthening of relatively few components.

Recent Developments in the Seismic Design of Bridges With Steel-Plate Girder Superstructures

Contrary to the provisions in many seismic design codes, plate girder superstructures of steel bridges should be explicitly designed for lateral load to ensure the adequacy of the load path from the deck above the girders to the bearings below. These structures should either be designed to behave elastically, or allow selected components to yield (e.g., end crossframes). In the latter case, significant reductions in the lateral shears transmitted to the substructures may be achieved, but special detailing of the connection between the crossframe and the deck is necessary to protect the girders from distortion and the girder-deck joint from degradation.

Composite Action in Steel Girder Bridge Superstructures Subjected to Transverse Earthquake Loading

Experiments are being performed on a 0.4 scale model of a steel girder bridge superstructure with a reinforced concrete deck to investigate means of improving the seismic performance of typical slab and girder bridges. During the early stages of experimentation, the need to understand the influence of composite action became apparent. Accordingly, an analytical study was undertaken. The first of several finite element analyses on a typical continuous four-span, four-girder bridge model assumed shear studs along the entire length of the bridge to provide full composite action. A second model omitted the shear connectors in the negative moment regions, a common design practice to avoid fatigue concerns in the top flange. It was found that the shear connectors in the fully composite model were sufficient to ensure composite action when subjected to transverse loading and provided an adequate load path through the superstructure and into the substructure. However, the lack of shear connectors in the negative moment regions caused the load to be transferred into the steel girders at the points of contraflexure, resulting in damage to these girders and inadequate formation of the ultimate limit state in the columns. The lack of composite action was also found to change the distribution of transverse shear forces in the cross frames, which is important for design of the end cross frames. Making the top chord of the cross frames composite with the deck, at the column bent locations, proved effective in minimizing damage to the superstructure.

Case Study of Tsunami Bore Impact on RC Wall

The Tohoku Tsunami of March 11, 2011 caused tremendous damage to many coastal buildings, bridges and port facilities. During field surveys following this event, the authors documented a number of structures that were damaged to a near-collapse condition as a result of hydrodynamic loading. Analysis of survivor videos provided information on the tsunami flow characteristics at these locations, allowing for an assessment of current hydrodynamic loading expressions under full-scale conditions.Based on laboratory experiments performed at Oregon State University, the lead author and colleagues developed a new hydrodynamic loading expression for a broken bore striking a vertical wall [1]. This expression was applied to a case study of a large vertical reinforced concrete (RC) wall damaged by an incoming bore strike during the Tohoku Tsunami. The damaged wall is on the seaward side of a high-bay building in the Minami Gamou Sewage Treatment plant near the Sendai coastline. A non-linear finite element model of the building was subjected to the hydrodynamic pressure distribution derived from the laboratory experiments. It is shown by structural analysis of the wall that using this loading expression generates the same yielding response in the wall as observed in the field, as reflected in the deflected shape measured by LiDAR. Similar analysis using current Japan Tsunami design provisions indicates that these provisions are considerably more conservative from a structural perspective than is necessary to resist hydrodynamic loading from a tsunami bore.This paper presents the application of hydrodynamic loading by the leading edge of a bore, determined based on laboratory experiments, to the non-linear analysis of a reinforced concrete building damaged during the Tohoku Tsunami.Copyright

Design of bridge falsework for gravity loads

Possible limit states associated with flange and web deformations in W and HP sections, and posts used in bridge falsework constructions are investigated in this paper. Critical limit states were found to be related to flange bending, post compression, and the interactions associated with complex patch loading. Other limit states are associated with web deformations. Two alternative methods based on yield line analyses that establish upper-bound limiting loads for these limit states are proposed. The first method accounts for an interaction between flange bending and post compression strength, whereas the second method uses an effective bearing area of the post. The critical web limit state was due to web yielding. Design recommendations and equations are presented with two design examples.