Ece Erdogmus

Strengthening Two-Way Reinforced Concrete Floor Slabs Using Polypropylene Fiber Reinforcement

Two methods for strengthening two-way reinforced concrete floor slabs subjected to out-of-plane bending loads are compared through experiments on seven test specimens and subsequent analyses. The seven test specimens were two unstrengthened regular reinforced concrete slabs (control), two slabs strengthened using glass-fiber-reinforced polymer (GFRP) sheets, and three slabs strengthened with an innovative method of applying a layer of fiber-reinforced cement (FRC) in varying thicknesses to the tension face of the slab. All specimens were 1.5  m×1.5  m (5  ft×5  ft) and were designed to resist bending in both directions. The advantages and disadvantages of the two strengthening methods are discussed in terms of structural considerations, e.g., increase in load carrying capacity and ductility, and construction considerations, e.g., economy and ease of application. Experimental results show a significant increase in the ultimate load capacity of all five strengthened slabs over the two control slabs. The FRC...

Recommendations for Design of Reinforced Concrete Pipe

Currently, two methods are available for the design of reinforced concrete pipes: the indirect design method and the direct design method. However, changes to indirect design procedures and proper application of the direct design method may not be well understood by designers. The goal of this work is to present designers with a concise history and major concepts of both methods to facilitate the proper application of either method for reinforced concrete pipe. The development of the indirect design method is given with emphasis on changes in the bedding factor, which is a constant that relates the strength of pipe in the three-edge-bearing test to the strength of pipe in the installed condition. The development of the standard installations and direct design method are presented, and finally a comparison between design results from both methods is made. Recommendations for reinforced concrete pipe design and the proper application of the bedding factor are provided. The direct design method is promoted a...

Accuracy of ground-penetrating radar for concrete pavement thickness measurement

Core extraction is the most common method for measuring concrete layer thickness in pavement construction. Although this method provides a very accurate thickness measurement, it is destructive, time-consuming, and does not provide adequate representation of the concrete layer thickness variability. Ground-penetrating radar (GPR) is a nondestructive evaluation technique that has been successfully used in several transportation applications, such as subsurface exploration and condition assessment. The main objective of this research is to investigate the accuracy and cost-effectiveness of using GPR in thickness measurement of concrete pavement for quality assurance purposes. A high-resolution 1.6-MHz ground-coupled antenna was used to perform grid scans and measure concrete thickness for several laboratory and field experiments. Results indicated that the use of metal objects underneath the concrete layer to improve bottom surface reflectivity was necessary for a reliable thickness measurement. Also, the use of calibration cores to determine the actual dielectric properties of the concrete was essential for accurate thickness calculation. An average accuracy of 98.5% was achieved when steel plates were used underneath the concrete layer and two cores were extracted for calibration. The effect of concrete age on GPR thickness measurement accuracy was also investigated.

Fiber Reinforced Mortar Mixtures for the Reconstruction and Rehabilitation of Existing Masonry Structures

The majority of the world’s architectural heritage encompasses unreinforced masonry structures, which are generally strong enough for the gravity loads, but are vulnerable against unexpected magnitudes of external out-of-plane loads and environmental effects. The recent trend of rehabilitating and strengthening unreinforced masonry with fiber reinforced polymer laminates, while effective, is not desirable in scenarios where aesthetics are important. Thus, there is a need for an equally effective yet aesthetically pleasing methodology. In this paper, the use of fiber-reinforced-mortars (FRMs) is proposed for masonry rehabilitation and reconstruction applications. Two types of fibers are considered; polyvinyl alcohol (PVA) fibers and novel organic fibers, such as corn silks. Several specimens with different type, size and volume fraction of fibers are tested in compression and flexure. Mixture proportions and the tested mechanical properties of each mixture are gathered in the form of a database. While the study is ongoing and the results are preliminary, it is found that certain volume fractions of PVA fibers are very effective in improving the toughness, ductility and durability of mortars. It is also found that corn silk FRMs show great potential for inexpensive and sustainable means to strengthen masonry structures.

Effect of polypropylene fiber length on the flexural and compressive strength of compressed stabilized earth blocks

Earthen masonry is generally brittle, weak and poor in damage resilience. There is historic evidence that natural fibers such as straw and horsehair have been used to reinforce earthen masonry to prevent desiccation cracks and improve tensile strength. However, fibers have also been known to negatively affect mechanical properties such as compressive strength (an important quality control parameter for load bearing masonry) by creating voids and lowering density. This paper reports on findings of a study directed at investigating the feasibility of avoiding such problems in compressed and stabilized earth blocks through optimizing the fiber length when using soil from Newberry, Florida. Standard polypropylene fibers were selected for the study. The two different lengths of fibers studied were 54 mm and 27 mm. The test results showed a general improvement in compressive strength of the fiber reinforced matrices compared to the unreinforced ones. While an improvement in modulus of rupture (MOR) was observed for matrices reinforced with 54 mm fibers, results varied for the other fiber-reinforced matrices. An improvement in post-initial crack behavior was observed for all fiber-reinforced matrices compared to the unreinforced ones. The 54 mm fibers yielded the best results based on the influence on MOR, compressive strength, and deformability compared to the other matrices. INTRODUCTION Earth has been used as a construction material since early civilization. Adobe, molded earth, wattle and daub, and cob are all forms of earthen construction that have been in existence for centuries. Globally, about a third of the human population resides in earthen shelters. In developing countries, the number is estimated to be as high as 50% (Minke, 2009).The use of locally available materials is highly encouraged by proponents of the green building movement. It is generally accepted that earthen masonry is a green material considering that at it uses indigenous soils 661 Construction Research Congress 2014 ©ASCE 2014

Polyvinyl Alcohol Fiber-Reinforced Mortars for Masonry Applications

This study describes how fiber-reinforced cementitious systems for concrete structures are increasing in popularity; however, fiber-reinforced mortar (FRM) mixtures for masonry applications have not been extensively studied. Various FRM mixtures using polyvinyl alcohol (PVA) fibers and FRM-clay unit prisms are tested and resulting mechanical properties are discussed in this study. The FRMs are developed specifically for masonry applications such as the rehabilitation, reconstruction, and strengthening of existing masonry structures; therefore, mixtures with low compressive strength and high ductility are desired. Results show that increased toughness, ductility, and energy absorption can be achieved using FRMs in masonry joints without significantly altering the compressive capacity or aesthetics of the structure. The results of the study point out the benefits of using FRMs in masonry applications in terms of improved mechanical characteristics, and provide valuable insight into effective FRM mixture design for masonry applications, suggested empirical formulas for modulus of rupture and modulus of elasticity, and directions for future research.

Timbrel Domes of Guastavino: Nondestructive Assessments On A Half-Scale Model

The Nebraska State Capitol in Lincoln (NE, USA) contains some of the best examples of timbrel vaults and domes utilizing the special Guastavino tile construction. A half-scale model of one of the concentric timbrel domes in the Nebraska State Capitol (called the Model Dome) is constructed at the Peter Kiewit Institute–Structures Laboratory of the University of Nebraska-Lincoln (Omaha campus). The experience of the construction of the Model Dome in itself is unique and therefore discussed in the article. After the Model Dome is constructed, experimental modal analysis is utilized as a nondestructive technique for updating three-dimensional computer models for this structure. As a result of this study, a validated three-dimensional finite element model of the Model Dome is obtained and several inferences are made regarding the construction, modeling, and dynamic testing of timbrel domes. The change in dynamic characteristics of a timbrel dome constructed with gypsum mortar due to environmental effects is also discussed.

Strength of Spandrel Walls in Masonry Arch Bridges

Previous research on the strength of masonry arch bridges has focused on the carrying capacity of the arch barrel in the span direction. Although the results of a spandrel wall collapse may be very serious, the transverse strength of masonry arch bridges has not been widely addressed. Recent experience, however, has shown that the transverse behavior and the strength of the spandrel walls are at least as important as the behavior in the span direction. Although complex computer analysis methods have been proposed for examining the masonry arch bridge as a three-dimensional structure, these methods are not suitable for everyday practical application. An approximate analytical method for the prediction of the strength of masonry spandrel walls is developed based on the conventional analysis of fills supported by retaining walls. The method is based on the determination of loads by Coulomb-Rankine analysis and the determination of resistance by the fracture line method, similar to the yield line method for reinforced concrete slabs. A table that further increases the simplicity and speed of the method is also provided. The proposed method allows the practicing engineer to calculate a factor of safety for the transverse strength of a spandrel wall for different situations, such as moist soil, cracked wall, effect of live load for shallow fill bridges, or existence of parapet walls. Results of these conventional, simplified analyses compare favorably with observed bridge distress and results of a previously validated finite element analysis method.

Horizontal Support Displacement of a Thin-Tile Masonry Dome: Experiments and Analysis

AbstractA half-scale physical model of a thin-tile masonry dome designed by Rafael Guastavino, Jr. that is located in the Nebraska State Capitol Building is constructed and tested both nondestructively and destructively to determine the load paths of the structure as well as the reactions at the support. A corner support of the model dome is incrementally displaced horizontally and the resulting crack locations are identified. Additionally, a linear finite element model of the dome, validated with experimental modal analysis, is modified to perform nonlinear analysis where loads are placed on the dome and the resulting stresses and reactions determined. The results from the nonlinear finite element model are then compared to the destructive testing carried out on the constructed physical model. From the results of both the nondestructive and destructive testing, it is determined that the thin-tile masonry dome in question acts as a pendentive dome, which exerts horizontal thrust as well as vertically tran...

Full Scale Test Installation for Reinforced Concrete Pipe

An experimental reinforced concrete pipe (RCP) installation is designed by University of Nebraska – Lincoln researchers and installed at the landfill of Lincoln, NE. The pipe installation consists of eight pipe segments, 48 in. (1219.2 mm) in diameter, installed under fill heights ranging from 5 ft (152.4 cm) to 20ft (609.6 cm). Pipe was designed according to a proposed design methodology, where, mostly the direct design method is followed while the 0.01” (0.254 mm) crack control criteria is eliminated. Four of the eight segments were over designed and the other four were under designed in terms of the height of fill they carry. Pipe segments were instrumented by eighty vibrating wire strain gages, and sixteen earth pressure cells. Field readings were obtained and monitored. The study is currently undergoing and the paper presents up-to-date findings of the experimental observations as well as inferences made regarding the RCP design considerations. Projected conclusions are such that the current design methods and criteria used for designing RCP are overly conservative.