Uncertainties and dynamic problems of bolted joints and other fasteners

Recent studies have highlighted the beneficial role of foundation uplifting and the potential effectiveness of guiding the plastic hinge into the foundation soil by allowing full mobilization of bearing capacity during strong seismic shaking. With the inertia loading transmitted onto the superstructure being limited by the capacity of the foundation, this concept may provide an alternative method of in-ground seismic isolation: the so-called rocking isolation. Attempting to unravel the effectiveness of this alternative design method, this paper experimentally investigates the nonlinear response of a surface foundation on sand and its effect on the seismic performance of an idealized slender single-degree-of-freedom structure. Using a bridge pier as an illustrative prototype, three foundation design alternatives are considered, representing three levels of design conservatism. Their performance is investigated through static (monotonic and slow-cyclic pushover) loading, and reduced-scale shaking ta...

http://ssi.civil.ntua.gr/downloads/journals/2012-ASCE_Soil%20%20Foundation%20Structure%20Interaction%20with%20Mobilization%20Bearing%20Capacity%20Experimental%20Study%20on%20Sand.pdf

Soil-Foundation-Structure Interaction with Mobilization of Bearing Capacity: Experimental Study on Sand

This article studies the seismic performance of a rocking-isolated bridge pier on surface foundation, resting on sand. A series of reduced-scale shaking table tests are conducted, comparing the performance of a rocking-isolated system to a pier founded on conventionally designed foundation. The two design alternatives are subjected to a variety of shaking events, comprising real records and artificial motions of varying intensity. In an effort to explore system performance in successive seismic events, three different shaking sequences are performed. Rocking isolation is proven quite effective in reducing the inertia forces transmitted onto the superstructure. The rocking-isolated pier is effectively protected, surviving all seismic excitations without structural damage, at the cost of increased foundation settlement. In contrast, a certain degree of structural damage would be unavoidable for the same system founded on a conventionally designed foundation. The rocking-isolated system is proven remarkably ...

/pdf/shaking-table-testing-of-rocking-isolated-bridge-pier-on-4yn3ft7y2z.pdf

Shaking Table Testing of Rocking—Isolated Bridge Pier on Sand

Adjacent precast, prestressed box girder bridges are widely used in the United States, but the shear keys between the girders tend to crack and leak. Three different shear key configurations were studied, i.e., a current detail where the shear key is approximately 10 in. (250 mm) from the top of the girder and grouted with non-shrink grout, this same detail grouted with epoxy rather than non-shrink grout, and a proposed mid-depth keyway grouted with non-shrink grout. The tests were conducted on a full scale, four-beam assembly which represented part of the bridge. The results showed that the currently used shear key detail cracks due to thermal stresses generated as the beams deflect upward and downward due to daily heating and cooling. The mid-depth shear key is less susceptible to these stresses and was found to be more resistant to cracking. Loading did not appear to cause new cracking, but rather seemed to propagate existing thermal cracks.

Full-scale testing of shear keys for adjacent box girder bridges

This paper presents the performance of constructed bridges in cold regions through examining the bridges in North Dakota that is one of the coldest regions in the United States. Unique approach of a combined multiple regression and geographic information system technology is employed to evaluate the performance and to identify the critical sources affecting deterioration of the 5,289 bridges sampled from the National Bridge Inventory database inspected between 2006 and 2007. Typical parameters examined include physical, material, and environmental factors associated with the existing bridges. The importance of maintenance and repair is highlighted. Traffic volume significantly influences the level of deterioration of the bridge decks. Year built is the most significant contribution to the structural deficiency of the bridges, followed by structural characteristics and traffic volumes. The presence of water particularly influences the deterioration. Concrete bridges are more durable than steel bridges. Tru...

Identifying Critical Sources of Bridge Deterioration in Cold Regions through the Constructed Bridges in North Dakota

This report describes a series of field tests of multibeam prestressed box girder bridges. The objective of the test was to investigate the in–situ performance of the grouted shear keys, located at the longitudinal joints between adjacent girders. The longevity of these joints can be a problem with this type of bridge; failure of the joint will typically not only compromise the load–sharing mechanism between adjacent girders, but also lead to the failure of the deck waterproofing system, with attendant corrosion problems. The tests consisted of monitoring relative displacements occurring across the intergirder joints, as well as bending strains in the girders themselves during passages of a preweighed tandem–axle dump truck, with axle loads typically in the range of 84.7kN (19 kips). Relative displacements were measured with an especially designed transducer, having a resolution on the order of 0.00254 mm (0.1 mil), which was bonded to the underside of the bridge across the intergirder joints. Bending strains in the girders were measured with conventional foil strain gauges, having a gauge length of 38 mm (1.5 in.) All bridges tested exhibited relative displacements across at least some of the joints, which indicated a fractured shear key.

Shear Key Performance in Multibeam Box Girder Bridges

The conceptual design of an innovative seismic-resistant steel framing system capable of providing stiffness and ductility to new or existing structures is presented. The bracing system consists of concentric X-braces connected in series with rectangular sacrificial shear panels. The braces are designed to remain elastic during seismic events while the shear panels are sized and configured to dissipate ample energy through plastic deformation-induced stable hysteretic behavior. Detailed three-dimensional nonlinear finite-element analyses using ABAQUS are performed to characterize and quantify the effects of the design parameters on the local response of the bracing system and to adjust the design so that potential buckling of the elements is mitigated. The finite element predicted force-displacement curves of bracing systems that achieve the desired local behavior when subjected to a specified interstory drift are in turn translated into a SAP2000 nonlinear link element. Embedment of the link elem...

Braced Ductile Shear Panel: New Seismic-Resistant Framing System

On September 11, 2006, “unusual” deflections of an overhead bridge-mounted sign support truss along IR 75 in Dayton, Ohio were reported. Investigation by Ohio DOT road crews revealed the complete fracture of two truss members near one of the truss supports. While total collapse did not occur, such an event could have catastrophic consequences along a major arterial roadway like IR 75. This concern, along with the fact that a similar failure occurred near Cleveland, Ohio in 2004, prompted an investigation that is the subject of this manuscript. Results of the investigation are based upon a combination of in situ field monitoring of traffic-induced bridge vibrations at the location of the failed sign support truss, finite-element simulation of the expected dynamic response of the original truss in such an environment, the length of service of the truss at the time of its failure, the volume of truck traffic on the bridge in question during that time of service, and metallurgical examination of the failed co...

Investigation of the Dayton, Ohio, IR 75 Sign Truss Failure of September 11, 2006

Fatigue demands often control design and detailing requirements of wind turbine support structures including the tubular steel tower. The in-situ structural demands placed on a community-scale (100kW) wind turbine have been monitored for approximately one year and the fatigue demands quantified using a Palmgren-Miner approach. A rain-flow counting method is used for calculating stress range cycles during turbine response. Demand-to-capacity ratios for a few common fatigue critical steel tower details are presented and can be used for estimation of remaining fatigue life. Future investigations will provide valuable data for evaluating fatigue loading based on aero-elastic analysis and for structural design requirements of wind turbine support structures.

Arthur A. Huckelbridge

Papers

Shear Key Performance in Multibeam Box Girder Bridges

Braced Ductile Shear Panel: New Seismic-Resistant Framing System

Investigation of the Dayton, Ohio, IR 75 Sign Truss Failure of September 11, 2006

In-situ measurements of fatigue demands on a wind turbine support structure

Overturning effects in stiffened building frames