Date of Award
Doctor of Philosophy (PhD)
The guidelines proposed by the NCHRP Report 350 pertaining to the safety of roadway hardware devices necessitated the evaluation of those devices. This study deals with the strength evaluation of precast concrete bridge railing.
A literature review was performed before the start of the study. Though many articles, reports, and publications were found regarding the testing of cast-in-place concrete barriers, such similar publications pertaining to precast concrete bridge railing were almost non-existent.
The theoretical work was performed using the yield line theory to predict the strength of the precast barrier. Though the theory was developed for cast-in-place barriers where the lateral impact force would be transferred to the reinforcement in the deck, there was no developed equations for evaluating the strength of the precast or bolted section. The theory was tested in this study.
The experimental work consists of the casting of the concrete barrier, evaluating the compressive strength of the concrete used in the precast barrier, transporting it to Louisiana Tech, and installing it in the strong floor lab. An instrumentation plan was developed and strain gauges were placed on both faces of the barrier in the intermediate and end regions. The barrier was subject to incremental static load until the barrier failed. Data were then collected and analyzed. The predicted ultimate strength of the barrier was obtained by using the yield line theory. The actual strength of the barrier was obtained on the static load testing that the barrier was subject to at the testing facility. The prediction of the ultimate strength of the concrete barrier was obtained by assessing the strength of the barrier at two locations: an intermediate region and an end region.
Computation shows that strength of the barrier at the end region is lower than that at an intermediate region. Even though the reinforcement pattern remained unchanged along and across the faces of the barrier, the section capacity of the barrier at the end region was smaller and thus, controlled the ultimate yield strength of the barrier. It is due to the end region being semi-continuous, unlike the intermediate region of the barrier.
The actual transverse force, Ft, that would cause a yield failure at the interior region, was 66 kips which is about one-third less than the predicated value using yield line theory (about 50 percent of cracks in the slab are not acceptable); while the computed transverse force that would cause a yield failure at the end region was 59 kips. Since the barrier collapsed as a result of the testing, the hydraulic ram could not be used to apply load at the end region.
It can be concluded that the ultimate capacity of a bolted section is lower than that of a cast-in-place concrete section when the developed yield line theory is applied. This result is due to the fact that the cast-in-place barrier transfers the applied load to the deck; whereas, the precast barrier's loads are resisted by the bolts through shear, uplift, or a combination of both.
It can also be concluded that the precast concrete barriers, like the one tested in this study, are not TL-3 compliant and their use should be limited to conditions that qualify for TL-2. This result is reserved for work zones and most local and collectorroads with favorable site conditions as well as where a small number of heavy vehicles is expected and posted speeds are reduced. Speed limit in work zones is limited to 45 mi/h.
Alaywan, Walid Rajab, "" (2011). Dissertation. 393.