Shear live load analysis of NEXT beam bridges for accelerated bridge construction

Using precast concrete elements in bridge structures has emerged as an economic and durable solution to enhance the sustainability of bridges. The northeast extreme tee (NEXT) beams were recently developed for accelerated bridge construction by the Precast/Prestressed Concrete Institute (PCI). To date, several studies on the live load distribution factor (LLDF) for moment in NEXT F beam bridges have been reported. However, the LLDFs for shear in NEXT F beam bridges are still unclear. In this paper, the lateral distributions of live load shear in NEXT F beam bridges were examined through a comprehensive parametric study. The parameters covered in this study included bridge section, span length, beam section, number of beams, and number of lanes loaded. A validated finite element (FE) modeling technique was employed to analyze the shear behavior of NEXT F beam bridges under the AASHTO HL-93 loading and to determine the LLDFs for shear in NEXT beam bridges. A method for computing the FE-LLDF for shear was proposed for NEXT beam bridges. Results from this study showed that the FE-LLDFs have a similar trend as the AASHTO LFRD-LLDFs. However, it was observed that some LRFD-LLDFs are lower than the FE-LLDFs by up to 14.1%, which implied using the LRFD-LLDFs for shear could result in an unsafe shear design for NEXT beam bridges. It is recommended that a factor of 1.2 be applied to the LRFD-LLDF for shear in NEXT F beam bridges for structural safety and design simplicity.

Seismic Performance of Pre-Fabricated Segmental Bridges With An Innovative Layered-UHPC Connection

Ultra-high-performance concrete (UHPC) has been regarded as promising alternative to provide reliable connections between difference segments (e.g., columns and pier footing/cap) during accelerated bridge construction (ABC) procedures. This paper proposes an innovative layered-UHPC connection for the pre-fabricated segmental (PFS) pier, whose seismic performance was validated through quasi-static experiment. The corresponding design procedure for PFS pier with this type of connections is presented based on the test results. The layered-UHPC connection ensures the emulative performance of pre-fabricated bridge as cast-in-place (CIP) ones, as well as provides greater economic efficiency than traditional UHPC connections. Based on experimental results, key issues concerning this connection, including the tensile behavior of UHPC, height of connection region, thickness of UHPC layer and steel bars in grouting bed, are presented and discussed. Then a seismic design procedure is proposed utilizing the capacity protection philosophy widely adopted in design specifications. The layered-UHPC connection is expected as capacity-protected component without damage, since it provides anchorage for steels extended from columns and pier cap/footing. While the pre-fabricated region is designed as ductile component undergoing nonlinearity during strong earthquakes. Following the detailed elaborations about the design philosophy, requirement and implementation steps, this procedure is further presented through illustration examples using PFS piers with various heights. The results show that PFS piers designed according to this procedure could meet the requirement under both frequent and rare earthquakes. Note that the PFS piers with this layered-UHPC connections could be designed similar to and emulative as CIP ones, which is believed friendly to designers in engineering practice.

Alternative Systems and Materials for Splicing Prestressed-Precast Concrete Piles

The use of piles is a common method for establishing deep foundations for bridges where there is a top layer of weak soil. Among various types of pile and installation methods, driving prestressed-precast concrete piles (PPCP) is a durable and economical option compared with the alternatives. Also, since the method employs pile segments prefabricated in precast plants and delivered to the site for installation, it conforms to the principles of Accelerated Bridge Construction (ABC) and provides a rapid alternative to other methods. However, often because of limitations on shipping and transportation, the length of precast prestressed pile segments that can be delivered to the bridge site has to be reduced. Also, headroom limitations for pile driving may limit the length of pile segments such that establishing adequate resistance may not be achieved with one segment. Therefore, splicing of pile segments has to be performed at the site to produce longer lengths. A study carried out as part of research activities at the Accelerated Bridge Construction University Transportation Center (ABC-UTC) at Florida International University has reviewed various types of available pile splices and attempted to build on the experiences gathered for ABC connections to introduce an alternative configuration for splicing PPCP segments. Accordingly, a variation of grouted bar splice was introduced and designed to provide PPCPs with a time-effective, economical, and labor-friendly method of splicing. The proposed connection is completely new for connecting PPCP segments. Because many of PPCPs are driven in a marine environment, the application of corrosion-resistant material at the splice system is also emphasized. The paper summarizes these investigations. The results of this study show that the newly developed systems can provide the required strength in bending, tension, and compression with smaller sizes and numbers of bars. It also makes the installation faster and easier compared with the current methods.

Effect of Fiber, Cement, and Aggregate Type on Mechanical Properties of UHPC

Ultra-High Performance Concrete (UHPC) is a new class of concrete that differentiates itself from other concrete materials due to its exceptional mechanical properties and durability. It has been used in structural rehabilitation and accelerated bridge construction, structural precast applications, and several other applications in the past decades. The mechanical properties of UHPC include compressive strength greater than 124 MPa (18 ksi) and sustained post cracking tensile strength greater than 5 MPa (0.72 ksi) when combined with steel, synthetic or organic fibers. Proprietary, pre-bagged mixtures are currently available in the market, but can cost about 20 times more than traditional concrete. This high price and the unique mixing procedure required for UHPC has limited its widespread use in the US and has motivated many researchers to develop more economical versions using locally available materials. The objective of this study was to investigate the effect of different proportions of typical UHPC mixture components on the mechanical properties of the mixtures. Particle packing theory was used to determine a few optimal mixture proportions and then modifications were made to investigate the effect. A compressive strength of around 124 MPa (18 ksi) was achieved without using any quartz particles in the mixture design. Doi: 10.28991/cej-2021-03091726 Full Text: PDF

Simplified method of analysis of adjacent precast “deck free” concrete box beams used in accelerated bridge construction

The prefabricated bridge is common method in construction since it provides controlled environmental conditions and long-term durability. These adjacent precast box beams are placed side by side with 15mm gaps, the top flanges connected with longitudinal shear keys poured on-site to assist in truckload distribution. Since the concrete-filled joints provide transverse shear rigidity, the load transferred from one beam to another takes place through transverse shear. A parametric study is conducted to investigate the accuracy of simplified analysis method in CHBDC for shear-connected beams to the adjacent box beams. A 3D finite-element was conducted on a wide range of box beams to obtain their magnification factors for moment and shear when subjected to truck loading. The obtained results were correlated with CHBDC and a more reliable simplified equations for distribution factors was developed. Special attention was given to the limitations of CHBDC simplified method and how it can be revised to include the adjacent box-beam.

Simplified method of analysis of adjacent precast “deck free” concrete box beams used in accelerated bridge construction

The prefabricated bridge is common method in construction since it provides controlled environmental conditions and long-term durability. These adjacent precast box beams are placed side by side with 15mm gaps, the top flanges connected with longitudinal shear keys poured on-site to assist in truckload distribution. Since the concrete-filled joints provide transverse shear rigidity, the load transferred from one beam to another takes place through transverse shear. A parametric study is conducted to investigate the accuracy of simplified analysis method in CHBDC for shear-connected beams to the adjacent box beams. A 3D finite-element was conducted on a wide range of box beams to obtain their magnification factors for moment and shear when subjected to truck loading. The obtained results were correlated with CHBDC and a more reliable simplified equations for distribution factors was developed. Special attention was given to the limitations of CHBDC simplified method and how it can be revised to include the adjacent box-beam.