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The anchorage zones of post-tensioned concrete members can be divided into local and general zones. The present study estimated the ultimate strengths of post-tensioned beams tested to anchorage failure using the AASHTO LRFD approximate stress analysis/design method, the critical section concept in which the strengths of the node-strut interface and local zone-general zone interface are examined, the bearing strength equation which considers the confinement effect due to reinforcing bars, and the nonlinear strut-tie model approach which incorporates nonlinear techniques in the selection, analysis, and verification processes of a strut-tie model, thereby evaluating their respective validity in the analysis and design of post-tensioned anchorage zones. The ultimate strengths of the post-tensioned beams in the nonlinear strut-tie model approach were estimated by checking the occurrence of a nodal zone failure mechanism, the structural instability of the selected strut-tie model due to the strength reduction of the struts and ties during the incremental loading steps, and conformity to the strut-tie model's geometric compatibility condition.

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The ultimate strength of simply supported reinforced concrete deep beams is governed by the capacity of the shear resistance mechanism. The structural behavior of the deep beams is controlled mainly by the mechanical relationships between the primary design variables including shear span-to-effective depth ratio, flexural reinforcement ratio, and the compressive strength of concrete. In this study, a simple indeterminate strut-tie model which reflects all characteristics of the ultimate strength and behavior of the deep beams was presented. A load distribution ratio, defined as the fraction of load transferred by a truss mechanism, was also proposed to help structural designers perform the rational design of deep beams by using the strut-tie model approaches of current design codes. In the determination of the load distribution ratio, a concept of balanced shear reinforcement ratio which ensures the ductile shear design of the deep beams was introduced, and the effect of the primary design variables was reflected through numerous numerical analyses of the presented indeterminate strut-tie model. In the companion paper, the validity of the presented model and load distribution ratio was examined by applying them to the evaluation of ultimate strength of 234 simply supported reinforced concrete deep beams tested to failure.