Reinforced Ecc - an Evolution from Materials to Structures

While significant advances have been made in concrete materials and in concrete structures over the last decade, research in materials and in structural engineering are often carried out separately. As a result, opportunities in major leaps in structural performance may be missed, or research emphasis in materials development may be misguided. This paper introduces the concept of integrated structures and materials design (ISMD), which links structural design and materials design via material mechanical properties. Specifically, an example of composite evolution from materials to structural systems illustrating the ISMD concept is presented, bridging the length scales associated with microstructures, composite materials and composite structures. The linking of these length scales suggests integrating composite materials design into design considerations for structures to improve their performance in terms of load-deformation response, energy absorption, deformability, structural stability, damage tolerance, construction efficiency (reinforcement detailing requirements), and rehabilitation needs. This approach is expected to benefit the safety and life-cycle cost of modern structures and enables innovative design solutions for demanding applications with severe environmental and loading conditions such as seismic resistant structures. The fundamental cause of structural damage in reinforced concrete (R/C) structures is the brittle deformation behavior of concrete in tension. The design of Engineered Cementitious Composites (ECC) is targeted at creating a fiber reinforced cementitious material with a deformation behavior analogous to that of metals, specifically at achieving pseudo strain-hardening and multiple cracking behavior. The combination of such a ductile cementitious composite with structural reinforcement (ductile steel or elastic Fiber Reinforced Polymers (FRP)) in direct tension results in deformation compatibility of these components in the reinforced ECC (R/ECC) composite, leading to a reduction of interfacial bond stresses and bond splitting cracks while maintaining composite integrity. The performance of R/ECC structural composites subjected to reversed cyclic flexural deformations greatly benefits from this deformation compatibility, resulting in a decrease of peak curvature at a given flexural deformation. Beyond localization of cracking in ECC, enhanced confinement, shear strength and buckling resistance in R/ECC members significantly reduce transverse steel reinforcement requirements and lead to stable energy dissipation by yielding of longitudinal steel reinforcement. Furthermore, R/ECC members with longitudinal FRP reinforcement show reduced residual displacements after unloading. On the structural system scale, the particular interaction of R/ECC members reinforced with steel and FRP reinforcement in a moment resisting frame provides a structural system with considerable energy dissipation capacity and reduced residual displacement. This composite structural system has a bi-linear elastic load-deformation behavior and auto-adaptive response capabilities. It is suggested that the opportunity for major advances in elevated performance of future generations of infrastructures is wide open using the ISMD approach.