Study of pergolas for energy savings in road tunnels. Comparison with tension structures

The huge consumption and environmental impact of electrical lighting in road tunnels in terms of energy, materials and maintenance, has evidenced the necessity of using solar light for tunnel lighting during daytime. One satisfactory solution has been to shift the threshold zone out of the tunnel by means of tension structures. Although pergolas in the portal gate of road tunnels have been mainly used for structural purposes, they have been also claimed as a co-lateral solution to achieve this target. In this work, the theoretical basis of the ad hoc use of pergolas for energy savings in road tunnels are developed, analyzed and compared with tension structures. General expressions for the light distribution under any arbitrary pergola, not reported in the reviewed literature for this study, are presented and the ESTS equation, used for energetic evaluation of tension structures, is also generalized to the case of pergolas. Finally, the accuracy of pergolas for normative compliance in matter of illumination is discussed and several important conclusions are presented. (C) 2013 Elsevier Ltd. All rights reserved.