【正文】 conglomerate of clay shale with inclusions of sandstone, basalt,and ash that is prone to landslide. As a sudsurface stratum the Cucaracha Formation is quite stable,but it quickly erodes when exposed to the elements. The engineers determined that deep foundations would therefore be needed for the western approach structure,the west tower,and the western piers. Before a detailed design of the foundationa could be developed,a thorough analysis of the seismic hazards at the site was required,The design seismic load for the project was developed on the basis of a probabilistic seismic hazard assessment that considered the conditions at the an assessment establishes the return period for a given earthquake and the corresponding intensity of ground shaking in the horizontal directtion in terms of an acceleration response PSHA determined two dominant seismic sources: a subduction source zone associated with the North Panama Deformed Belt capable of producing a seimic event as strong as ,and the Rio Gatun Fault, capable of producing an event as strong as . The NPDB event was used as the safety evluation earthquake,that is,the maximum earthquake that could strike without putting the bridge out of damage to the bridge would be minor but would require some closures of the Gatun Fault event was used as the foundational evaluation earthquake,a lowerlevel temblor that would cause minimal damage to the bridge and would not require the FEE load case,the SEE loading was scaled back by FEE is assumed to have a peak acceleration of and a return period of 500 years。 the probability that it will be exceeded within 50 years is 10 pencent and within 100 years,18 SEE is assumed to have a peak acceleration of and a return period of 2,500 years。the probability that it will be exceeded within 50 years is 2 pencent and within 100 years,4 persent. Because of uncertainty about the direction from which the seismic waves would approach the site, a single response spectruma curve showing the mathematically puted maximum response of a set of simple damped harmonic oscillators of different natural frequencies to a particular earthquake ground accelerationwas used to characterize mitions in two mutually orthogonal directions in the horizontal conduct a timehistory analysis of the bridge’ s multiple supports,a set of synthetic motions with three ponentslongitudinal,transverse,and verticalwas developd using an iterative ground motions from an earthquake in Chile in 1985 were used as “ seed” motions for the sythesis process. A time delay estimatethat is,an estimate of the time it would take for the motions generated by the SEEand FEE earthquakes to travel from one point to the nextwas create using the assumed seismic wave velocity and the distance between the piers of the an assumed was velocity of approximately ,a delay on the order of half a second to a second is appropriate for a bridge 1 to 2km long. Soilfoundation interaction studies were performed to determine the stiffness of the soil and foundation as well as the seismic excitation measurement that would be used in the dynamic studieswere conducted by means of soilpile models using linear and nonlinear soil layera of varying equivalent pile lengths in the studiesthat is, the lengths representing the portions of a given pile that would actually be affected by a given earthquakeinduced ground motionranged such a threedimensional model,there are six ways in which the soil can resist the movement of the lpile because of its stiffness:throngh axial force in the three directions and through bending moments in three the bridge site contains so many layers of varying soil types,each layer had to be represented by a different stiffness matrix and then analyzed. Once the above analyses were pleted,the International engineerstaking into consideration the project requirements developedby the owenerevaluated several different concrete cablestayed number of structural systems were investigated,the main variables,superstructure cross sections,and the varying support conditions described above. The requirement that the evevation of the deck be quite high strongly influenced the tower the proposed deck elevation of more than 80m,the most economical tower shapes included singleand dualmast towers as well as “ goal post” towersthat is,a design in which the two masts would be linked to each other by crossbeams. Ultimately the engineers designd the bridge to be wide with a 420mlong cablestayd main span,two 200mlong side spansone on each side of the main spanand approach structures at the ends of the side the east side there is one 46m long concrete approach structure,while on the west side there are three,measuring 60,60,and 66m,for a total bridge length of 1, side spans are supported by four piers,referred to,from west to east,as ,P3,and P4. The bridge deck is a continuous singlecell box girder from abutment to abutment。 the expansion joints are located at the abutments only. Deck movements on the order of 400 mm are expected at these modular expansion joints Multidirectional pot bearings are used at the piers and at the abutments to acmodate these movements. The deck was fixed to the two towers to facilitate the balancedcantilever method of construction and to provide torsional rigidity and lateral restraint to the deck.. Tra