Capacity reduction and Fire Load Factors for LRFD of Steel Members Exposed to Fire

A general reliability-based methodology is proposed for developing capacity reduction and fire load factors for design of steel members exposed to fire. The effect of active fire protection systems (e.g., sprinklers, smoke and heat detectors, fire brigade, etc.) in reducing the probability of occurrence of a severe fire is included. The design parameters that significantly affect the fire design of steel members are chosen as random variables. Raw experimental data published in the literature was analyzed to obtain the statistics of parameters for which no statistical information was available in the literature. Model errors associated with the thermal analysis models are also characterized based on experimental data. It is found that uncertainty associated with the fire design parameters is significantly higher than that of room temperature design parameters. To illustrate the proposed methodology, capacity reduction and fire load factors are developed for simply supported steel beams in U.S. office buildings, and it is shown that for consistent reliability these factors should vary depending on the presence of active fire protection systems in a building

Sensors to Monitor CFRP/Concrete Bond in Beams Using Electrochemical Impedance Spectroscopy

The use of inexpensive electrochemical impedance spectroscopy based sensor technology for nondestructive evaluation (NDE) of bond degradation between external carbon fiber-reinforced polymer (CFRP) reinforcement and concrete is examined. Copper tape on the surface of the CFRP sheet, stainless steel wire embedded in the concrete, and reinforcing bars were used as the sensing elements. Laboratory experiments were designed to test the capability of the sensors to detect the debonding of the CFRP from the concrete and to study the effect of short-term (humidity and temperature fluctuations) and long-term (freeze-thaw and wet-dry exposure and rebar corrosion) environmental conditions on the measurements. The CFRP sheet was debonded from the concrete, and impedance measurements were taken between various pairs of electrodes at various interfacial crack lengths. The dependence of the impedance spectra, and of the parameters obtained from equivalent circuit analysis, on the interfacial crack length was studied. Capacitance parameters in the equivalent circuit correlated strongly with the interfacial crack length and can be used to assess the global state of the bond between CFRP sheets and concrete. Impedance measurements taken between embedded wire sensors can be used to detect the location of debonded regions

Electrochemical-Mechanistic Model for Concrete Cover Cracking Due to Corrosion Initiated by Chloride Diffusion

A holistic electrochemical-mechanistic model of the corrosion of steel reinforcing bars inside concrete that accounts for the diffusion of oxygen and moisture into the concrete and rust layers, the densification of rust due to confinement, the flow of rust into the concrete pores, the development of internal pressure due to rust buildup, and cracking of the concrete cover is presented. The relationship between the corrosion current and the pressure buildup due to the corrosion products for different concrete cover thicknesses and concrete quality was calibrated through experiments using an accelerated corrosion test with an applied current. Results from finite-element analysis with an inelastic smeared crack concrete model were used to calibrate a simple analytical model of the critical internal pressure required to cause cracking of the concrete cover. The various submodels are linked together to predict the time for cracking of the concrete cover from the time of corrosion initiation. Results of parametric studies using the model indicate that the main factors that control the corrosion current and the time to cracking are the boundary condition, water-cement ratio, and concrete cover

Flexural Behavior of Reinforced Concrete Beams Strengthened with CFRP Sheets and Epoxy Mortar

Experiments were conducted to study the effect of using epoxy mortar patch end anchorages on the flexural behavior of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) sheets. More specifically, the effect of the end anchorage on strength, deflection, flexural strain, and interfacial shear stress was examined. The test results show that premature debonding failure of reinforced concrete beams strengthened with CFRP sheet can be delayed or prevented by using epoxy mortar patch end anchorages. A modified analytical procedure for evaluating the flexural capacity of reinforced concrete beams strengthened with CFRP sheets and epoxy mortar end anchorage is developed and provides a good prediction of test results

Freeze-thaw Durability of Concrete Columns Wrapped with FRP and Subject to Corrosion-Like Expansion

Experiments were conducted to assess the effects of using fiber-reinforced polymer (FRP) wraps, with fibers oriented in the hoop direction, for rehabilitating corrosion-damaged columns. This paper reports findings related to the freeze-thaw durability of concrete specimens with round and square cross sections, wrapped with glass and carbon FRP, after they are subjected to an internal expansive force similar to that generated by corroding steel. The results of the experiment indicate that freeze-thaw cycles have no statistically significant effect on the compressive strength of glass- and carbon-wrapped specimens. Freeze-thaw conditioning generally reduced the longitudinal failure strain of wrapped specimens. The square wrapped specimens had lower compressive strength compared to the round specimens, even though the cross-sectional area of the square prisms was higher than that of the round cylinders. This is because of the reduced confinement provided by the wraps for square cross sections and stress concentrations that develop at the corners. Wrapped square prisms always failed by rupture of the wrap at a corner. A reduction of approximately 30 to 40% in failure stress was noted between wrapped specimens with round and square cross sections, respectively

Application of Noise Cancelling and Damage Detection Algorithms in NDE of Concrete Bridge Decks Using Impact Signals

Delamination is a commonly observed distress in concrete bridge decks. Among all the delamination detection methods, acoustic methods have the advantages of being fast and inexpensive. In traditional acoustic inspection methods, the inspector drags a chain alone or hammers on the bridge deck and detects delamination from the “hollowness” of the sound. The signals are often contaminated by ambient traffic noise and the detection of delamination is highly subjective. This paper describes the performance of an impact-based acoustic NDE method where the traffic noise was filtered by employing a noise cancelling algorithm and where subjectivity was eliminated by introducing feature extraction and pattern recognition algorithms. Different algorithms were compared and the best one was selected in each category. The comparison showed that the modified independent component analysis (ICA) algorithm was most effective in cancelling the traffic noise and features consisting of mel-frequency cepstral coefficients (MFCCs) had the best performance in terms of repeatability and separability. The condition of the bridge deck was then detected by a radial basis function (RBF) neural network. The performance of the system was evaluated using both experimental and field data. The results show that the selected algorithms increase the noise robustness of acoustic methods and perform satisfactorily if the training data is representative

Response of an Arch Dam to Non-Uniform Excitation Generated by a Seismic Wave Scattering Model

Non-uniform ground motions are generated based on a single record available at a site and seismic wave scattering analysis. The Chino Hills 2008 earthquake records at the Pacoima Dam site are used to indicate the accuracy of the method. Dynamic analysis of the Pacoima dam-reservoir-foundation under uniform and non-uniform ground motions is carried out using the EACD-3D2008 software, and the results are compared to recorded responses at different locations on the dam. There is good agreement between computed and recorded displacements of the dam for non-uniform excitation. For uniform excitation, the displacements are underestimated in comparison with those obtained from recorded excitation. Significant intensification of stresses, especially near the foundation, and different patterns of stress distribution are observed for non-uniform excitation in comparison with uniform excitation. For uniform excitation maximum stresses occur in the crown cantilever near the crest, but for non-uniform excitation the maximum stresses occur along the sides and near the foundation

College-Wide First Year and Career Mentorship Programs

The College of Engineering at the University of New Haven began two formal mentorship programs in spring 2020 with the help of a for-profit company named Mentor Collective. The First-Year Mentorship Program is designed for students entering the university and the Career Mentorship Program is designed for juniors and seniors. The programs were sponsored by a generous gift from Sikorsky, a Lockheed Martin Company. This paper focuses particularly on the impact of the First-Year Mentorship Program on the first to second year retention of engineering and computer science students

Full-scale Experimental Modal Analysis of an Arch Dam: The First Experience in Iran

Forced vibration field tests and finite-element studies were conducted on the Shahid Rajaee concrete arch dam in Northern Iran to determine the dynamic properties of the dam–reservoir–foundation system. The first forced vibration tests on the dam were performed with two different types of exciter units, with a limited maximum force, bolted on the dam crest for alternative in-phase and out-of-phase sequencing. Because of an insufficient number of recording sensors, two arrangements of sensors were used to cover sufficient points on the dam crest and one gallery during tests. Two kinds of vibration tests, on–off and frequency sweeping, were carried out on the dam. The primary natural frequencies of the coupled system for both symmetric and anti-symmetric vibration modes were approximated during on–off tests in two types of sequencing of exciters, in phase and out-of-phase, with a maximum frequency of 14 Hz. The principal forced vibration tests were performed at precise resonant frequencies based on the results of the on–off tests in which sweeping around the approximated frequencies at 0.1 Hz increments was performed. Baseline correction and suitable bandpass filtering were applied to the test records and then signal processing was carried out to compute the auto power, cross power and coherence spectra. Nine middle modes of vibration of the coupled system and corresponding damping ratios were estimated. The empirical results are compared against the results from calibrated finite-element modeling of the system using former ambient vibration tests, considering the dam–reservoir–foundation interaction effects. Good agreement is obtained between experimental and numerical results for eight middle modes of the dam–reservoir–foundation system

”CyberWorld” as a Theme for a University-wide First-year Common Course

Nowadays we all live in a cyber world and use the internet for emailing, banking, streaming video, shopping, reading news, or other activities. Given all the time people spend online, it is important that all students (regardless of their major) learn some basics about living in a cyber world, e.g., strategies for online safety, impact of artificial intelligence, digital forensics or ancestry.com. To facilitate students from many majors to learn about important issues related to the internet, eight faculty from a variety of disciplines at the University of New Haven integrated the theme of Cyber World into our team-taught, first-year experience course, also referred to as the “Common Course.” The Common Course’s primary purpose is to enable students to develop evidence-based arguments and to challenge their own and others’ assumptions in relation to that evidence. Each Common Course class focuses on a broad topic (e.g., Justice, Happiness, or Identity) that instructors use as a touch point to facilitate critical thinking. In Cyber World, however, the topic is given stronger focus, and all students in the class are expected to come away with specific cyber-related knowledge. A special challenge is that the majority of the 160 students are from non-STEM majors. Given the varied background of students, this course covers a variety of topics such as sharing DNA with ancestry.com, protecting against identity theft, detecting fake news, and oversharing personal information. The course is taught by eight faculty members from four different colleges having expertise in a variety of disciplines. An important side effect of this faculty diversity is that interdisciplinary collaborations among faculty are promoted. Our paper has three significant contributions: (1) We present the eight topics related to living in a cyber world that we chose for this course, including our rationale for why they are appropriate and relevant; (2) We summarize how we integrated the Cyber World topics into the structure of the Common Course, which includes a discussion of the challenges we faced; and (3) We summarize some initial results on how students perceived their experience as well as how they performed compared to other common course sections / topics