Pavement subgrade is an in-situ material upon which the pavement structure is constructed. A soil with a high plasticity index will experience high shrinkage and swell depending upon its moisture content with detrimental impacts on its supported pavement structure. Removing and replacing the weak soil with better-quality soil is an alternative to stabilization of poor subgrade soil and may be a very expensive solution, typically for large road networks. Secondly, stabilization of weak soil -subgrade using conventional cement may not be sustainable due to its high CO₂ footprint. The feasibility of this non-conventional method using blended geopolymer binder for stabilization of weak subgrade soil was investigated compared to the conventional cement stabilization method. Laboratory testing of design mixes included unconfined compression test, maximum dry density, CBR and shrink & swell testing determining its feasibility and optimum extent. This research paper will present the findings on the effectiveness of blended geopolymer (fly ash and slag) as an alternative to conventional cement-based soil stabilizers for weak subgrade and its sustainability potential.

The Joint ACI-ASCE Committee 445 published a document titled Report on Torsion in Structural Concrete that contained an in-depth review of historical theory development, design models, and simplified design procedures for the effect of torsion in concrete structures. That document contained three design examples that were relatively simple. An important goal of this ACI Special Publication is to provide more realistic design examples that are usable by design professionals. This paper satisfies that goal by showing a detailed solution to a realistic example that has been encountered on several occasions by one of the authors. Another goal of the ACI Special Publication is to show applications where torsion is combined with flexure and shear. In this example, the torsional effects are combined with biaxial flexure and biaxial shear forces. This example includes a check of the new provisions in ACI 318-19 for bi-axial shear effects.

This paper shows a detailed solution for the design of a reinforced concrete grade beam subjected to torsional effects combined with biaxial shear and biaxial flexure. The grade beam is a portion of a structural screen wall system. A 25 psf (1.20 kPa) strength level wind pressure acts on a 20 ft (6.10 m) tall CMU wall supported by a continuous grade beam. The 21 in (533 mm) wide by 18 in (457 mm) deep grade beam is isolated from an expansive soil and is supported by drilled shafts 21 ft (6.40 m) on center. The wind load and gravity loads induce torsion, biaxial bending moments, and biaxial shear forces in the grade beam. This example shows how to calculate the internal forces in the grade beam at the critical section and design the required longitudinal and shear reinforcement according to the ACI 318-19 code.

The design of the grade beam includes closed stirrups of #4 (Ø 12) bars spaced at 5.5 in (140 mm), five #8 (Ø 25) bars used near the top and bottom faces and one #6 (Ø 16) bar used at mid-height near the side faces.

The use of a Performance-Based Seismic Design (PBSD) approach to design buildings that exceed 240-feet (73.2 m) tall has been common among many west coast cities. More recently, Oakland, California has been an epicenter of development that has created a market for taller buildings. The residential tower at 1640 Broadway, which is currently under construction, is the first tower designed using PBSD exceeding 240-feet (73.2 m) tall in Oakland. This is notable in terms of establishing the implementation of PBSD in a new jurisdiction. This is also notable because of the near fault location of Oakland, given that the Hayward fault is less than 3.1 miles (5 km) from the downtown region, which raises new issues such as fault normal/fault parallel ground motion scaling issues and designing for extremely high demand levels. Due to these extreme demand levels, the project consisted of high reinforcement ratios within the walls and embedded steel coupling beams. Finally, the foundation conditions were challenged by the proximity to BART tunnels and therefore consist of a hybrid mat foundation supported on deep soil mixed panels and cased steel piles. A summary of the unique aspects of the building are presented and compared with typical code compliant and PBSD towers.

This paper will present the challenges and unique aspects associated with increasing the capacity of one of the container wharves at Barbour’s Cut Terminal to support new Ship-to-Shore (STS) container cranes with gage lengths of 100 ft. (30 m), which was an upgrade from the previous container cranes that featured 50-ft. (15 m) gage lengths. The design criteria included achieving an additional 50 years of service life from the existing elements and new elements; therefore, the assessment results and techniques used for service life modeling will be discussed. In the new structural elements, service life modeling was used to determine the necessary concrete mixture characteristics, including use of fly ash and corrosion-resistant reinforcement, to achieve the required service life.

This paper will also discuss the design approach, including the use of springs to represent the soil-structure interaction, for determining the demands on the various components. In addition, the interaction between the new structure and existing structure and the resulting torsion will be discussed. Finally, various lessons learned from using strut-and-tie modeling, including the relative stiffness of the chord elements and need for three-dimensional modeling, will be summarized.

Bridge embankments serve a vital role in raising the roadway profile to the bridge deck elevation for passage of vehicles. It is common practice to construct embankments utilizing compacted lifts of soil obtained from nearby borrow pits. Soil borrowed from regions of predominantly expansive clay soils can be problematic for bridge embankment construction. High plasticity soils swell in contact with moisture, inducing vertical and lateral pressure on embankments. Mechanically Stabilized Earth (MSE) walls are particularly susceptible to soil expansion as they try to confine high soil expansion pressures through soil reinforcement and mobilization of a stabilized volume behind the face of the wall. This paper provides insight into the investigation of MSE wall movement, abutment movement and corresponding bridge beam distress, and reinforced concrete failures resulting from high plasticity soil backfill in existing bridge embankments. Remediation strategies are discussed which are directed at the expansive soil behavior within the embankment.