In the past half century (since the famous Tacoma Narrows Bridge failure), the art of wind design for long-span bridges has progressed considerably from the overall examination of physical models to a progressively more analytical view, in which the mechanisms affecting bridge stability and performance are identified. During this process, which has been aided by succinct mathematical formulations, the essential minima of required experimental data have progressively been defined with some degree of clarity.  In this presentation, a review of the state of the art of wind engineering for long-span bridges will be given, using the newly completed Akashi-Kaikyo Bridge (1991m main span) in Japan as an example application. In addition, unresolved or problematic issues remaining will be identified and outlined, including a brief description of current research efforts that are attempting to address them.

In addition, and overview of other important and relevant projects in wind engineering at JHU will be presented in brief.

The increasing number of important high performance concrete (HPC) structures, where there is a risk of fire, is encouraging further studies on the mechanical behavior of both materials and structures, either at high temperature or after cooling.  A typical example is the R/C liner of the railway tunnel across the British Channel, which suffered a highly disruptive fire in the southbound shaft in November ’96, luckily with no human losses, but with extensive structural damages, which forced the shutdown of the shaft for several months.  As a matter of fact, on the whole High-Performance Concrete is more temperature-sensitive than Normal-Strength Concrete, mainly because of its lower and less-interconnected porosity, which favors steam pressure build-ups accompanied by extensive micro cracking, localized spalling and lower strength at the aggregate-mortar interface.  Furthermore, because of the widely different properties of the many HPC mixes now available, it is difficult to generalize the results of each single research project on HPC.

With regard to HPC exposed to high temperatures, 3 different projects have been funded lately in Milan, in cooperation with the Italian Energy Agency (ENEA), Imperial College (London, UK) and Italian No. 1 cement producer, within the framework of 2 BRITE-EURAM projects. The high-temperature and residual properties of several cementitious materials have been studied experimentally (Compression, tension, fracture parameters; high-strength concrete; very high-strength microconcrete and mortar; with/without fibers), and the residual behavior of two sets of relatively-small structures (deep beams and slabs) has been investigated as well, in order to have some information on what extent the material decay may affect the structural behavior. Finally, R/C eccentrically-loaded sections have been studied with the aim of working out (a) the ultimate M-N envelopes for different fire durations, and (b) a few “performance indicators” to make comparisons with NSC sections. The conclusion is that – in spite of its greater temperature-sensitivity – HPC performs more than satisfactorily within the structural framework, even more so if polymeric fibers are added to the mix.

Leakage of groundwater into tunnels and underground repositories is a very common problem that tunnellers have to face during the construction operations. In case of heavy inflows, the construction operations can be dramatically delayed or even stopped, causing economic losses for all parties involved. Experience from tunneling in hard rocks, limestone and chalk, have shown that the total construction cost can increase by 25%, 35% and  60%, respectively due to water inflow. However, depending on the purpose of  the facility, even the smallest dripping can be of importance.Dripping into  underground nuclear repositories located in unsaturated rocks, for example,  should be fully understood due to the serious consequences that can have on its total performance in isolating the nuclear waste.

Starting from the nineteen-seventies an increasing number of underground facilities have been constructed for public use and for storing waste and products hazardous for the environment. As a result, more research has been devoted to studying the leakage and flow of groundwater into underground constructions and the hydraulic behaviour of fractured rock masses around underground repositories for nuclear waste, oil or gases, or around mines.

The necessity to come up with quantitative and precise descriptions of the rate and direction of flow around such facilities combined with the exponential increase in computer capabilities have pushed towards the development and use of an increased number of computer-based predictive tools. All this has brought to associate the concept of prediction to computer simulations and numerical models. Sophisticated numerical models fitting the capabilities of the most advanced personal computers can in fact be used during many of the most challenging groundwater problems to produce results that are used as a basis for decision-making. But despite the effort made, much uncertainty still surrounds the prediction process.

However, a basic requirement to produce reliable models is to have a clear and realistic picture of the hydrogeological and hydraulic conditions around the underground construction. Unfortunately, this is a seldom case, since the uncertainty surrounding the prediction process is mostly given by the three following factors: the limited amount of geological and hydrogeological information that is usually available, the large number of geological, hydrogeological, and hydraulic parameters that play a role in the inflow mechanism and the degree of heterogeneity of the hydrogeological system.

This presentation, by showing the result of research conducted at the Bolmen tunnel, Southern Sweden, at the Pont Ventoux tunnel, Northern Italy and at the Yucca Mountain project, the planned long-term US underground repository for nuclear waste located in Southern Nevada, shows how these three factors can influence the reliability of predictions.

Two devastating seismic events occured recently within a period of three months in Northwestern Anatolia which lies on the well-known North Anatolian Fault Line. The first one occurred on August 17th, 1999, with a magnitude of 7.4 on the Richter scale and caused apocalyptic damage including 25,000 dead. Many industrial facilities were affected creating a catastrophic economic situation for the whole country. The second one occured on November  12th, 1999, with a magnitude of 7.2 on the Richter scale. It affected a less populated area causing smaller mortality than first, but it still generated a huge regional economic loss.

Various types of structural hazards were observed especially in connection with poor soil behaviour under seismic action. Problems of land use and settlement for the newly and quickly urbanising areas, as well as quality control issues in construction activities came under scrutiny. National and international attention also became focused on problems of repair and stabilising.
This presentation will summarize observations on these main issues and on some other lessons emerging from follow-up studies in the disaster areas.

This presentation briefly summarizes research works on adaptive on-line identification of nonlinear structural systems using input-output measurement data (accelerations).  The proposed adaptive identification algorithm, based on the recursive least-square method, has been implemented for both parametric and non-parametric identification studies.  For the case of no a priori information on the type of the structural model, an analytical method based on a power series of multivariable polynomial expansions has been introduced.  The effectiveness and robustness of the proposed methodology has been shown in various numerical simulations, considering the effects of excitation amplitude, of large sampling time interval, of measurement noise, of a priori mass estimation error, and of exact-, under-, and over-parameterization of the structural model.

The National Airport Pavement Test Facility at the FAA’s William J. Hughes Technical Center began operation in April 1999.  The NAPTF is the only facility of its type in the world designed to test full-scale pavement sections to failure under simulated aircraft gear loads with full position and wander control. The presentation will describe briefly the program of full-scale pavement tests being conducted at the NAPTF, and show how the data collected are being used by the FAA to support the development of advanced pavement design procedures for airports.  The FAA’s LEDFAA design procedure, released in 1995, uses layered elastic (Burmister) analysis to compute critical stresses and strains for airport pavement design. New design procedures now being developed by the FAA will implement 3D finite element structural analysis to compute highly realistic responses to multiple-wheel gear loadings.  In order to take full advantage of the improved analytical capabilities of these advanced design procedures, updated failure models are needed.  The tests now being conducted at the NAPTF will provide crucial performance/failure data for airport pavements built to accommodate large commercial aircraft with main gear assemblies of six wheels or more.

SEA is a technique for predicting vibrational energy flow through structures due to broadband, stochastic excitation. AutoSEA2 is a user-friendly, general-purpose code which implements SEA. It is widely used in a diverse set of industries (automotive, space, aircraft, maritime) and is increasingly used in commercial and home building industries. The figure below shows a typical result from an AutoSEA2 analysis.

This seminar will give an overview of SEA and then a demonstration of the AutoSEA2 code.