Flexural Behavior of Precast Concrete Segmental Box-Girders with Dry Joints

Precast concrete segmental (PCS) box-girders are widely used in bridge construction, while studies on flexural behaviors of PSC box-girders with dry joints are insufficient. Six large-scale PCS box-girders with dry joints were tested to failure under two-point loading in this study. Strain increments, tendon forces, deflections at mid-span, and cracks were recorded during the tests. Multiple factors were investigated with regards to their influence on flexural performance of girders. It is found that most specimens failed due to the excessive force in tendons, while the specimen with external tendons failed due to concrete compressive crushing. Larger shear span ratio resulted in greater increase in tendon force and concrete strain during loading and, accordingly, the lowest ultimate flexural capacity. Lower concrete strength resulted in larger increase in concrete strain and tendon force during loading and relatively smaller deflection at failure. For the specimen with four segments, a significant increase in tendon force and smaller deflections at failure was observed as compared with specimen 1, though the failure load was similar. Numerical simulation is further conducted, where it is found that the area of prestressed tendon and the number of joints have a significant influence on ultimate flexural bearing capacity and deflection; besides, deflection control standard of PCS girders should be stricter than that of the integral cast girder. The corbel joints, in general, show better ultimate performance than the castle-shaped joints.

Improving the Installation Criterion for Concrete Coated Pipelines

Current design practice limits the concrete strain to approximately 0.2% in a simplified design criterion. In most standard cases, this has proved to be safe and adequate. However, in recent years, the pipeline industry is extending into more remote, harsher environments and larger diameter pipelines. The use of the simplified design criterion has, in some circumstances, resulted in too strict installation requirements which limit the number of relevant installation vessels. This paper presents some findings on the concrete strain for submarine pipelines with concrete weight coating (CWC) derived from the numerical program performed within the scope of Phase 1 of the joint industry project “Design of concrete coating for submarine pipelines”. Non-linearities in the concrete weight coating, anti-corrosion coating (ACC) and steel material properties, as well as large deformation and the sequence of load application were included in the numerical model. The results from the numerical analyses have been well validated against existing experimental data, and the numerical model was subsequently used in an extensive parametric study, where the behaviour of concrete coated pipelines was investigated for monotonic and reversed bending with nominal strain up to 0.4%. These numerical results can be used to widen the applicable range of the simplified concrete crushing criterion in DNVGL-ST-F101 (2017), and to formulate a rational approach for the design of pipeline concrete weight coating under typical installation and operation conditions. The rational design approach will allow for a wider range of installation vessels to select from for installation of the pipeline, and relaxation of the installation weather window criterion.