Anil Patnaik

Nonuniform Corrosion-Induced Stresses in Steel-Reinforced Concrete

Understanding of cracking behavior of cover concrete is important for assessment of the remaining service life of corrosion-affected concrete structures. Predicting initiation of concrete cracking is commonly based on the evolution of stresses caused by the volume expansion of corrosion products on reinforcing bars. This paper presents an analytical method that is capable of providing the solution to two-dimensional (2D) elastic stress field caused by nonuniform volume expansion around the corroding reinforcing bars. The developed method features the formulation of a displacement model, which is applied as a boundary condition to simulate the effect of nonuniform corrosion on the deformation of the surrounding concrete. A closed-form solution to the stress field is obtained using the complex variable method of Muskhelishvili. Validation of the solution is supported by a comparison with finite-element-based simulation results. The solution reveals the evolution of stresses surrounding two typical locations...

Probabilistic modelling of the bond deterioration of fully-grouted rock bolts subject to spatiotemporally stochastic corrosion

Developing predictive models for quantitative assessment of the deterioration of rock bolts exposed to corrosive environments is essential for rational planning of maintenance activities for anchorage structures. This article presents a probability-based computational model for predicting the time-dependent deterioration of bond capacity of corroding rock bolts due to the attack of chlorides. The inherent stochastic nature involved in the corrosion and degradation process is identified and simulated. A method is developed based on fundamental Mohr–Coulomb theory to evaluate the effect of corrosion on the bond strength due to a failure mode involving splitting of grout cover. Parameters affecting both strength and stress state at the bolt–grout interface are quantitatively related to the degree of corrosion. Integrating the realised corrosion stochastic process and the developed bond loss evaluation method, a computational algorithm based on Monte Carlo simulation is presented for evaluating the bond deterioration in a probabilistic framework. The presented model is used in an illustrative example to show its capability to trace the evolution, throughout the entire design life, of several representative performance indicators of rock bolts as a structure unit or of the interested location within the anchor length.

Mechanisms Governing Fatigue, Damage, and Fracture of Commercially Pure Titanium for Viable Aerospace Applications

In this paper, the cyclic stress amplitude controlled high-cycle fatigue properties and final fracture behavior of commercially pure titanium (Grade 2) are presented and discussed. The material characterization was developed and put forth for selection and use in a spectrum of applications spanning the industries of aerospace, defense, chemical, marine, and commercial products. Test specimens were prepared from the as-received plate stock of the material with the stress axis both parallel (longitudinal) and perpendicular (transverse) to the rolling direction of the plate. The test specimens were cyclically deformed at a constant load ratio of 0.1, at different values of maximum stress, and the corresponding cycles-to-failure is presented. The cyclic fatigue fracture surfaces were examined in a scanning electron microscope to establish the macroscopic fracture mode, the intrinsic features on the fatigue fracture surface, and the role of applied stress-microstructural feature interactions in governing failu...

On the Use of Gas Metal Arc Welding for Manufacturing Beams of Commercially Pure Titanium and a Titanium Alloy

A noticeable reduction in the cost of structural components made from titanium, both commercially pure and the alloy counterpart is possible with the concept of built-up welded fabrication. Rolled sheets of the titanium material can be welded together to fabricate a built-up structural component without having to machine the part from a large billet. In this paper, the results of a recent feasibility study on the manufacturing of welded built-up I-beams for large structural applications are presented and discussed. The fillet welds were produced using the pulsed Gas Metal Arc Welding (GMAW-P) process. Commercially pure titanium (Grade 2) and a titanium alloy (Ti-6Al-4 V) were the two materials chosen for the study. The specific details of the welding process are highlighted along with a discussion of the successful implementation of the concept of built-up welded beams for the manufacture of large structural elements and components of titanium.

Correlation of strength of 75 mm diameter and 100 mm diameter cylinders for high strength concrete

Abstract Results of statistical analysis of test data are presented to establish if there is a correlation between the strength of 75- and 100-mm-diameter cylinders for concrete with strength between 110 and 160 MPa. A linear regression analysis showed that strength measured on 75-mm cylinders is within 5% of the corresponding strength measured on 100-mm cylinders. A more detailed analysis of the difference between the mean strengths of the two sizes of cylinder of each group of the tests indicated that 75- and 100-mm cylinders measure the concrete strength within 4%. It is concluded that 75-mm cylinders are suitable for compressive strength testing of high strength concrete (>100 MPa). For strength of concrete greater than 150 MPa, 75-mm cylinders are likely to measure smaller concrete strength than the corresponding 100-mm cylinders.

Plastic Shrinkage Reduction Potential of a New High Tenacity Monofilament Polypropylene Fiber

This paper presents the evaluation of a new high tenacity monofilament polypropylene fiber for the reduction of plastic shrinkage cracks in concrete. The crack reduction potential of the fiber was studied using cement-rich concrete and the performance of the fiber was compared with that of three other presently available fibers (Fiber B, Fiber C, and Fiber D). Performance of these fibers was evaluated by comparing the area of plastic shrinkage cracks developed in control slabs (with no fibers) with the crack area of fiber reinforced concrete slabs. For example, the reduction of the crack area due to the addition of the new high tenacity monofilament fiber was 91 percent for a dosage of 0.593 kg/m(3) [1.0 lb/yd(3)], 86 percent for 0.297kg/m(3) [0.5 lbs/yd(3)] and 57 percent for 0.196 kg/m(3) [0.33 lbs/yd(3)]. The results indicate that the new fiber with fiber length of about 18 mm[3/4 inch], and a fiber dosage of 0.593 kg/m(3) [1.0 lb/yd(3)] was most effective in reducing the plastic shrinkage cracks in concrete. For the same fiber quality, three other fibers were less effective in reducing cracks.

Compression buckling behavior of 7075-T6 aluminum skin stiffened panels fabricated by friction stir welding

Friction Stir Welding (FSW) of skin stiffened structures is being developed as a rivet replacement technology in the aerospace industry. Preliminary research was done on compressive strength and deformation characteristics of FSW aluminum skin stiffened panels. 7075-T6 aluminum sheets were bent to form stiffeners and friction stir welded to 7075-T6 aluminum sheets to fabricate two FSW panels. Another stiffened panel of similar dimensions was made by using traditional riveting. The compression test results and the failure modes of the panels are presented in this paper. The tests revealed that the FSW panels failed at approximately 17% higher load than the riveted panel. The failure loads of the FSW test panels were within 3 to 10% of the predicted load obtained by using two existing theoretical methods, and the failure load of the rivet panel was within 11 to 20% of the predicted load.

Process Parameter Development and Fixturing Issues for Friction Stir Welding of Aluminum Beam Assemblies

Friction Stir Welding (FSW) is being developed as a rivet and resistance spot welding replacement technology for aerospace and aircraft structures. While the FSW process is at a high Technology Readiness Level (TRL) and is being implemented on selected DOD and NASA hardware components, it has not seen extensive application due to limitations in the understanding of the design constraints and fixturing issues associated with a producible design. This paper describes the preferred FSW joint types and designs for beam structures which facilitate production implementation. The effects of fixturing and tooling on the FSW process development needs and resultant joint properties are discussed along with examples of fixturing and tooling approaches for fabrication of aluminum stiffened beam assemblies.

Full-Scale Testing and Performance Evaluation of Rockfall Concrete Barriers

Rockfall hazards are present throughout the state of Ohio. The Ohio Department of Transportation (DOT) employs Test Level 3 standard concrete barriers along the edges of roadways to contain rockfalls in high-risk areas. The performance of these barriers under impact from rocks on the ditch side and their effectiveness for rockfall catchment are relatively unknown. Full-scale impact tests were performed on concrete barriers to simulate the effects of impacts from rocks of various sizes and shapes. Numerous impacts were made at different sections and levels of the barriers to test their structural integrity and energy absorption capacity. The results from this study revealed that 32-in.-high precast concrete barriers with current Ohio DOT details had an impact energy absorption capacity of up to 24 kJ under a single impact. The corresponding energy absorption capacity of 42-in.-high cast-in-place concrete barriers was about 56 kJ under a single impact. Moreover, these barriers experienced severe cracking and spalling of concrete under impact loading. Several design modifications were studied in this test program. These modifications included reducing the spacing of rebars and rebar sizes, using welded wire fabric, and using different types of fibers in the concrete. The tests conducted on the modified concrete barriers showed an impact energy increase of more than 100% with the modifications suggested in this study. Barriers made from the modified designs also experienced significantly reduced extent and severity of cracking and a reduction in spalling and splashing of concrete under impact loading.

Quasi-Static, Cyclic Fatigue and Fracture Behavior of Alloy Steel for Structural Applications: Influence of Orientation

In this paper, the results of a study aimed at understanding the extrinsic influence of test specimen orientation, with respect to a wrought alloy-steel plate, on the stress-controlled cyclic fatigue properties and fracture behavior of a structural steel is highlighted. The alloy steel chosen was ASTM A572 grade 50. Samples of this alloy steel, prepared from both the longitudinal and transverse orientations, were cyclically deformed over a range of maximum stress and the corresponding number of cycles to failure (NF) was recorded. The influence of test specimen orientation and intrinsic microstructural effects on cyclic fatigue life and fracture behavior are presented and discussed. Overall, the macroscopic fracture mode was essentially identical regardless of orientation of the test specimen with respect to the wrought plate. The microscopic mechanisms governing cyclic deformation, fatigue life, and final fracture behavior are presented in light of the mutually interactive influences of magnitude of applied stress, intrinsic microstructural effects, orientation of test specimen, and deformation characteristics of the key microstructural constituents.