BAY BRIDGE

MTC Bay Bridge Rail Feasibilty Study

APPENDIX B. DATA / SPECIFICATIONS

The following is a select list of documents found in the Caltrans' archives or within ongoing work which were used in this study:

• The original design specifications from the 1930's titled State of California Department of Public Works, San Francisco Oakland - Bay Bridge, Design Specifications, Superstructure
• The design specification for the rail removal from 1957 titled State of California Department of Public Works, Division of San Francisco Bay toll Crossings, Specifications for Design, Reconstruction of San Francisco Oakland - Bay Bridge
• Structural capacity design calculations performed in 1965 and 1967 for the 1959 through 1963 reconstruction - referenced in this report as the 1965/67 Investigation.
• Excerpt from the Yerba Buena Island Structural Calculations - Contract #4029
• San Francisco-Oakland Bay Bridge, East Span Seismic Safety Project, contract 59A0040 DESIGN CRITERIA Draft 4-9-99

The 1965 and 1967 calculations are the most complete source of final design information. Within this work the loads and allowable stresses are defined and the demand stresses are calculated for most of the main structural components. These values will be used throughout this study as the basis for assessing increased and decreased service load demands and capacities under various rail scenarios. The Design Criteria for the East Spans is a very thorough document that establishes the live loads and allowable stresses. Comparison of loads within these criteria and the loads from the proposed rail addition will be undertaken.

The governing specifications for this feasibility study are:

• State of California Department of Transportation Bridge Design Specifications
• San Francisco-Oakland Bay Bridge, East Span Seismic Safety Project, Contract 59A0040 DESIGN CRITERIA Draft 4-9-99

Evolution of the Design Live Loading
Typical HS20-44 lane loads (U.S. Standard Highway Load) have a magnitude of 640 pounds per linear foot. Standard practice is to reduce these values recognizing that each lane will not be loaded from end to end or not all lanes will be loaded side by side with the maximum truck weights. Similarly, the cross-lane 'C' factor is a load reduction factor that acknowledges the improbability of full size trucks in each of the three or more lanes simultaneously.

In the 1930's specifications, these reductions were dictated in the design specifications. By the time the 1959 work started, the paper "Live Loadings for Long-Span Highway Bridges" by J.R. Ivy et al appeared in the ASCE Proceeding Vol. 79 dated June1953. This article set down the parameters and intensities for live load as a function of span length. AASHTO had also introduced a 'C' factor for the multiple lane structures. Table 1 contains those loads and factors, which were incorporated into the 1965/67 Investigation.

Today, the West spans would be designed to criteria similar to that currently employed on the Proposed East Span Design. Those long span live load intensity values are shown in Table 2. For spans similar to the West spans of the Bay Bridge, the changes between the 1953 ASCE paper and the 1999 criteria create a further decrease in the live loads.