There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

United States. National Oceanic and Atmospheric Administration (Postdoctoral Fellowship Program)

Physically-based Assessment of Hurricane Surge Threat under Climate Change

Utilization and efficiency of ground granulated blast furnace slag on concrete properties – A review

Our knowledge to model, analyse, design, maintain, monitor, manage, predict and optimise the life-cycle performance of structures and infrastructures under uncertainty is continually growing. However, in many countries, including the United States, the civil infrastructure is no longer within desired levels of performance and safety. Decisions regarding civil infrastructure systems should be supported by an integrated reliability-based life-cycle multi-objective optimisation framework by considering, among other factors, the likelihood of successful performance and the total expected cost accrued over the entire life-cycle. The primary objective of this paper is to highlight recent accomplishments in the life-cycle performance assessment, maintenance, monitoring, management and optimisation of structural systems under uncertainty. Challenges are also identified.

Life-cycle performance, management, and optimisation of structural systems under uncertainty: accomplishments and challenges 1

This study proposed the vision-based system which remotely measures dynamic displacement of bridges in real-time using digital image processing techniques. This system has a number of innovative features including a high resolution in dynamic measurement, remote sensing, cost-effectiveness, real-time measurement and visualization, ease of installation and operation and no electro-magnetic interference. The digital video camera combined with a telescopic device takes a motion picture of the target installed on a measurement location. Meanwhile, the displacement of the target is calculated using an image processing technique, which requires a target recognition algorithm, projection of the captured image, and calculation of the actual displacement using target geometry and number of pixels moved. For the purpose of verification, a laboratory test using shaking table test and field application on a bridge with open-box girders were carried out. The test results gave sufficient dynamic resolution in frequency as well as the amplitude.

A vision-based system for remote sensing of bridge displacement

This paper compares results from dynamic live load tests using the non-contact laser Doppler vibrometer (LDV) system with those from two types of contact sensors. Bridge girder deflections and vibrations are simultaneously measured using a linear variable differential transducer (LVDT)-cable system (deflection) and geophone sensors (velocity), both attached to the girders, and the LDV, equipped with displacement and velocity signal decoders. Live load tests are performed on a 3-span continuous unit of the 9-span Doremus Avenue Bridge Replacement Project using 5-axle trucks of known weight and configuration. The Doremus Avenue Bridge is a composite steel slab-on-girder construction. Bridge response is compared for two of the 10 girders. Overall, the LDV measurements of deflection and velocity compare very well with those recorded by the contact sensors and may be used as an alternative to the two systems. Other advantages and disadvantages are also highlighted.

Comparison of laser Doppler vibrometer with contact sensors for monitoring bridge deflection and vibration

Ultra-high-performance concrete (UHPC) is a type of cement-based composite for new construction and/or restoration of existing structures to extend service life. UHPC features superior workability, mechanical properties, and durability compared with conventional concrete. However, some challenges limit the wider application of UHPC, such as low workability for large-volume production, high autogenous shrinkage, insufficient flexural/tensile properties, and unpredictable durability after concrete cracking. Therefore, this paper reviews the state-of-the-art technologies for developing UHPC mixtures with improved properties. This review covers the following aspects: (1) the existing design methodologies; (2) the typical ingredients (e.g., binders, aggregates, chemical admixtures, and fibers) for preparation of UHPC and the underlying working principals; (3) the technologies for improving and controlling key properties (e.g., workability, autogenous shrinkage, compressive performance, tensile/flexural properties, and durability); and (4) the representative successful applications. This review is expected to advance the fundamental knowledge of UHPC and promote further research and applications of UHPC.

New development of ultra-high-performance concrete (UHPC)

New perspectives on recycling waste glass in manufacturing concrete for sustainable civil infrastructure

The modulus of elasticity of a material is a fundamental property required for the proper modeling of its constitutive behavior and for its proper use in various structural applications. This paper discusses experimental evaluation of the elastic modulus of high-performance concrete made from mixes using various percentages of fly ash, silica fume, and granulated blast furnace slag. Results are compared to those from control specimens at various ages between 1 and 90 days. The results presented are part of a study for the New Jersey Department of Transportation (NJDOT) to develop and implement High-Performance Concrete (HPC) mix design and technical specifications for transportation structures. The study also investigates the effect of curing on the elastic modulus. Three methods of curing were evaluated: (1) air-dry curing, (2) curing compound, and (3) wet curing with burlap. The results showed that adding silica fume resulted in an increase in strength and modulus at early ages, however, there was no change in the modulus at 28 and 56 days. In addition, adding 20% fly ash with various percentage of silica fume had an adverse effect on both strength and modulus values at all ages to 90 days. It is also shown that dry curing and curing compound reduce the modulus of elasticity compared to wet curing with burlap. Results showed the elastic modulus of HPC is proportional to the compressive strength, but the prediction equations of ACI-318 and ACI-363 may not accurately predict the modulus values for high-performance concrete with pozzolans.

Effect of pozzolanic materials and curing methods on the elastic modulus of HPC

The deterioration of bridges due to increased traffic loading, progressive structural aging, and reinforcement corrosion from severe weathering conditions has become a major problem around the world. External prestressing is considered one of the most powerful techniques used for strengthening or rehabilitation of existing structures and has grown to occupy a significant share of the construction market. This paper presents the results of an analytical investigation of the strength and structural behavior of concrete members prestressed with external tendons. The behavior at both the serviceability and ultimate limit states is evaluated. A nonlinear analysis model, based on the incremental deformation method, is developed to predict the entire response of concrete members originally designed with or strengthened by external prestressing. The proposed analysis reproduced experimental results of deflection and tendon stress responses with remarkable accuracy. A parametric study was undertaken to evaluate the behavior of concrete beams either designed using external prestressing or strengthened by it. The analytical results demonstrated that the second-order effect, associated with the progressive change in eccentricity of the tendons with increasing member deformation, is the main factor that distinguishes the behavior of external tendons from an internal unbonded tendon system. Because of this effect, undeviated external tendons mobilized lower nominal flexural resistance and inelastic deflections than did deviated tendons. When used for strengthening concrete flexural members, providing a moderate amount of external prestressing steel leads to significant deflection recovery, some reduction in the live load deflection, and a substantial increase in the yield load and ultimate flexural capacity of the members.

Hani Nassif

Papers

Comparison of laser Doppler vibrometer with contact sensors for monitoring bridge deflection and vibration

New development of ultra-high-performance concrete (UHPC)

New perspectives on recycling waste glass in manufacturing concrete for sustainable civil infrastructure

Effect of pozzolanic materials and curing methods on the elastic modulus of HPC

Externally Prestressed Members: Evaluation of Second-Order Effects