Computational Modeling of Translucent Concrete Panels Aashish Ahuja 1 ; Khalid M. Mosalam, M.ASCE 2 ; and Tarek I. Zohdi 3 Abstract: The last decade has witnessed a heightened interest in making buildings more sustainable, which has been fueled largely by the increase in energy costs and advancements in manufacturing technology. Lighting consumes a substantial amount of this energy, making it necessary to look for alternative technology that depends more on natural lighting. This study investigated a novel building envelope material that consists of optical fibers embedded in concrete. The fibers are used to channel solar radiation into the building to reduce the dependence on artificial lighting especially during peak time. This paper presents a geometrical ray-tracing algorithm to simulate light transmission properties of the proposed translucent concrete panel. It was concluded that a tilt angle of 30° for the panel transmits the maximum amount of light among all the tilt angles considered. Using this tilt angle, the rate at which sunlight radiation is absorbed by the panel was calculated, and a preliminary study was conducted to estimate the solar heat gain coefficient of the panel for possible use in place of a glazing material by the construction industry. DOI: 10.1061/(ASCE)AE.1943-5568.0000167. © 2014 American Society of Civil Engineers. Author keywords: Concrete panel; Daylight capture; Energy efficiency; Ray tracing; Simulations; Solar heat gain; Structural wall; Translucent concrete. Introduction Buildings (commercial and residential) consume almost 41% of the total energy that is available for use in the United States. A large part of this energy, in the form of electricity, is used solely in artificially lighting the indoors of buildings (DOE 2011). The electric energy is derived primarily from thermal power plants that are not clean sources and contribute to greenhouse gas emissions. An innovation like translucent concrete (TC) captures and delivers daylight into build- ings, which could reduce our dependence on indoor lighting and save electricity. Such technology can be constructed as a part of a building envelope (i.e., wall and roof), because it satisfies requirements that are usually set apart (Mosalam et al. 2013): (1) envelope behaving as a structural subsystem, (2) construction procedure is simple and scalable, and (3) movable and mechanized parts are avoided. Com- pared with a traditional electric lighting system, illuminating the indoors with daylight also creates a more appealing and healthy environment for building occupants (Edwards and Torcellini 2002). In this paper, the authors used available sunlight data in esti- mating the light-transmitting capabilities of TC. The computational model of a TC panel consists of a grid of plastic optical fibers (OFs) embedded in concrete, allowing light to be transmitted through the otherwise opaque panel. Daily simulations were carried out at intervals of 30 min between 8 a.m. and 5 p.m. The results for the whole year were collected to infer the panel’s transmissibility of direct and diffused sunlight. Based on the simulation results, the heating rate of the panel was estimated for different times of the year. Previous Work on TC In 2001, Hungarian architect Aron Losonzi invented LiTraCon, the first commercially available form of TC. It was a combination of op- tical fibers and fine concrete, combined in such a way that the material was both internally and externally homogeneous. It was manufactured in blocks and used primarily for decoration. The current price of a LiTraCon block (100 mm thick) is approximately 2,140 Euro=m 2 (Ex Works), which makes it prohibitively expensive and difficult to commercialize. During the World Expo 2010 Shanghai China, Italy modeled its pavilion out of TC using approximately 4,000 blocks. The blocks were rather heavy to be used as a facade sub- system in buildings. Another product featured plastic fibers ar- ranged in a grid, namely Pixel Panels, developed by Bill Price of the University of Houston. These panels transmitted light in a pattern resembling thousands of tiny stars in the night sky. University of Detroit Mercy also developed a process to produce translucent panels made of portland cement and sand and reinforced it with a small amount of chopped fiberglass. These panels, which were only 2.5 mm thick at their centers, were thin enough to be translucent under direct light. The primary focus of the TC technology previously has been on its aesthetic appeal and its application in artistic design. Recently, He et al. (2011) published a study on smart TC, which experi- mentally explored the light emission properties of TC in the labo- ratory. Building on his research, this study took a step further by modeling light transmission and studying heating rate of the TC panel when exposed to sunlight throughout the year. Interestingly, development of light-transmitting facades is gaining more interest. Recently, a study on a novel translucent facade made from organic materials like sucrose was published (Gutierrez and Zohdi 2014). Theory and Modeling Illumination and Irradiation Calculations for the TC Panel The sky is described as a Perez model (Perez et al. 1987) that estimates the global irradiance (or illuminance) on a tilted surface. Global irradiance (G) is the sum of direct horizontal (G b ) and diffuse (G d ) components of the sunlight irradiance, given as 1 Ph.D. Candidate, Dept. of Mechanical Engineering, Univ. of California, Berkeley, CA 94720-1740. E-mail: aashishahuja@berkeley.edu 2 Professor, Dept. of Civil and Environmental Engineering, Univ. of Cal- ifornia, Berkeley, CA 94720-1710 (corresponding author). E-mail: mosalam@ berkeley.edu 3 Professor, Dept. of Mechanical Engineering, Univ. of California, Berkeley, CA 94720-1740. E-mail: zohdi@me.berkeley.edu Note. This manuscript was submitted on March 18, 2014; approved on October 20, 2014; published online on November 11, 2014. Discussion period open until April 11, 2015; separate discussions must be submitted for individual papers. This paper is part of the Journal of Architectural Engineering, © ASCE, ISSN 1076-0431/B4014008(8)/$25.00. © ASCE B4014008-1 J. Archit. Eng. J. Archit. Eng. Downloaded from ascelibrary.org by UNIVERSITY OF CALIFORNIA on 11/17/14. Copyright ASCE. For personal use only; all rights reserved.