## 1 Introduction  
Reinforced concrete (RC) members subjected to high sustained loads may experience time-dependent failure. This in turn may cause all or part of a building to collapse. RC members can be exposed to levels of sustained load higher than typical service levels because of design errors, construction errors and material deterioration. [PERSON] [1] showed that, under a high sustained stress (over 75% of its short-term strength), plain concrete can experience a compressive failure. However, the time-dependent strength and stiffness characteristics of concrete members with reinforcement under high sustained load have not been fully investigated. Previous research has only tested a limited number of beams and those tests did not include compression reinforcement. This research provides valuable experimental data on the behavior of shear-controlled reinforced concrete beams loaded under high levels of sustained load to fill in the lack of previous studies. The objective of this study is to understand the effect of high sustained gravity loads on the behavior of RC shear-controlled beams and thus better understand the collapse mechanism of buildings under high sustained loads. The research program is designed to evaluate the time-dependent strength and stiffness characteristics of RC shear-controlled beams, determine the level of high sustained load that would lead to eventual failure (collapse) in RC shear-controlled beams, and evaluate the characteristics of impending failure. This research is motivated by building collapses in service under sustained gravity loads. These buildings experienced total or partial collapse without additional loading, such as an earthquake or change in use. [PERSON] and [PERSON] [2] reported 172 structural collapses in low-rise and multistory buildings in the U.S. from 1989 to 2000. Partial or total failure accounted for 94% of these collapses and 45% were related to design or construction error, overloading, or material insufficiency. [PERSON] [3] reported 604 collapses in the U.S. from 1975 to 1989, excluding those caused by natural hazards. Technical errors were blamed for 78% of the collapses and 86% of collapses occurred to RC buildings. The collapses caused 416 deaths. In contrast, according to USGS [4], earthquakes have caused 68 deaths in the U.S. since 1990. [PERSON] [5] reported 150 collapses around the world from 1977 to 1981. Of those, about 65% were related to RC structures. These data highlight that although uncommon, structural collapse does occur in RC buildings under sustained gravity loads. Several collapses have occurred in parking garages where material degradation led to high sustained loads (loads close to capacity) in RC members. One example is the New York Wilson Hospital parking garage, a flat-plate structure, that failed in 2015 [6]. Corrosion in the reinforcement reduced the capacity of the slab-column connection. This led the concrete to experience a load level close to its capacity and eventually to failure under sustained load. Although material degradation is a significant contributor to the collapse, this research focuses on the behavior of RC members under high sustained stresses to determine the effects of sustained load on collapse. In other cases, collapse or near collapse occurred in buildings where construction errors or poor material quality led to high sustained loads in RC members. In the Dolphin Tower condominium, a 15-story RC flat-plate building in Sarasota, Florida structural failure was temporarily avoided. The structure experienced severe damage to the 4 th-floor slab because of poor concrete quality. Collapse was avoided through temporary shoring, but it took nearly 5 years to repair because the functionality and safety condition could not be judged based on available knowledge [7]. Greater knowledge about how RC members behave or how concrete is damaged under high sustained loads may have helped the structural safety evaluation of the building.