International Concrete Abstracts Portal

Through a Change Proposal by Facca Incorporated, the Ontario Ministry of Transportation (MTO) approved the replacement of the as-tendered steel H-piles by newly designed prestressed/precast Ultra-High-Performance Concrete (UHPC) piles for supporting the west abutment of the Lily River Detour Bridge. The 300 mm (~12”) deep UHPC piles were designed and installed at the west abutment based on the previous successful development and testing of a tapered H-shaped pile at Iowa State University. The east abutment, as tendered, was designed to be supported by six steel H-shaped battered piles driven to bedrock. For the west abutment, six UHPC piles were produced and installed using the same batter. Since the site contained occasional boulders and the design intent to drive the piles to bedrock, the UHPC piles were fitted with steel shoes for the first time. All piles were successfully installed to reach the targeted load bearing capacities. After the replacement bridge was constructed, the detour bridge was removed and the UHPC piles were extracted to examine the conditions of the piles. This presentation will provide details of the innovative design of the piles, fabrication and driving of the piles, and lessons learned from analyzing the driving data and removal of the piles. Fellowship and Scholarship recipients. With the help of generous donors from the concrete community, the ACI Foundation awards high-potential undergraduate and graduate students in engineering, construction management, and other appropriate curricula.

The cement industry recently marked the second anniversary of the Portland Cement Association’s (PCA’s) Roadmap to Carbon Neutrality. The article highlights PCA’s efforts in achieving carbon neutrality by co-hosting a panel event during Climate Week NYC 2023 and engaging with the federal government on policies to promote the development of carbon capture, utilization, and storage technologies.

The first part of this month’s two-part Q&A explains neglecting the size-effect factor per Section 13.2.6.2 of ACI 318-19 and whether it applies to pile caps. The second part discusses if wet setting of reinforcement is allowed per ACI 318-19 or other relevant ACI documents.

The “Notional Pile” formulation is developed for modeling a group of piles in a foundation. It is a new procedure for foundation modeling for dynamic analysis in conformance with ACI 351.3R. It is an augmentation of the well-known Novak procedure. Foundation stiffness is represented as a set of notional pile elements. This differs from conventional procedures in which the pile group stiffness is represented by a set of springs lumped at one point. With notional piles and finite element modeling of the cap, flexible-cap modes of vibration can be extracted. With conventional procedures, only lower-frequency rigid body modes can be extracted. Notional piles distribute stiffness more realistically and enable cap-pile interaction. A specific case is used to illustrate the new procedure. For that case, the cap did not have a regular distribution of mass or stiffness. Dynamic loads were applied with considerable eccentricity, at multiple locations and with multiple frequencies. Notional piles accommodated these irregularities. The notional pile formulation was validated by comparing measured to computed foundation responses. The comparison was good but not great. The foundation was to be reconfigured for new machinery. The retrofit design was modeled using notional piles. Responses were computed and compared to applicable limits.

Many common building materials, such as concrete and steel, are understood to experience a change in apparent material properties under high strain rates. This effect is often incorporated into impact and blast design by using dynamic increase factors (DIFs) that modify properties of the material such as strength and stiffness when subjected to high strain rates. There is currently limited guidance on dynamic properties of fiber reinforced polymer (FRP) sheets bonded to concrete. Since FRP is a common retrofit material for blast and impact load vulnerable structures, it is important to have a full understanding on the behaviour of the FRP material and of the composite action between the FRP sheet and the substrate it is bonded to. Important parameters for blast and impact resistant design of reinforced concrete structures retrofitted with surface bonded FRP include dynamic measures of debonding strain, development length, and bond stress. This paper presents the results of an experimental program measuring the dynamic properties of carbon fiber reinforced polymer (CFRP) sheets bonded to concrete under impact induced high strain rates.

A series of rectangular concrete prisms were cast and fitted with surface bonded CFRP sheets to facilitate pull-out shear tests that directly measure the FRP to concrete bond. The bonded length of the CFRP sheet was variable with three different lengths explored. A series of static tests have been conducted to measure the strain fields on the FRP sheets under load up to failure. These strain fields, which were measured with digital image correlation techniques, were used to determine development length, bond stress, and ultimate strain of the FRP sheet prior to debonding. A companion set of prisms have also been cast and will be tested under impact loading to explore the same properties at high strain rates of around 1 s-1. Initial test results indicate a potential increase in both ultimate strain and bond stress, and a decrease in development length under high strain rates. The results of the larger study will be compiled and, when compared with the static companion set, be used to propose DIFs for FRP sheets bonded to concrete for use in design in high strain rate applications.

However, the main constitutive phases of SHCC, i.e. matrix, fibers and interphase between them, are highly rate sensitive. Depending on the SHCC composition, the increase in loading rates can negatively alter the balanced micromechanical interactions, leading to a pronounced reduction in strain capacity. Thus, there is need for a detailed investigation of the strain rate sensitivity of SHCC at different levels of observation for enabling a targeted material design with respect to high loading rates.

The crack opening behavior is an essential material parameter for SHCC, since it defines to a large extent the tensile properties of the composite. In the paper at hand, the rate effects on the crack opening and fracture behavior of SHCC are analyzed based on quasi-static and impact tensile tests on notched specimens made of three different types of SHCC. Two SHCC consisted of a normal-strength cementitious matrix and were reinforced with polyvinyl-alcohol (PVA) and ultra-high molecular weight polyethylene (UHMWPE) fibers, respectively. The third type consisted of a high-strength cementitious matrix and UHMWPE fibers. The dynamic tests were performed in a split Hopkinson tension bar and enabled an accurate description of the crack opening behavior in terms of force-displacement relationships at displacement rates of up to 6 m/s (19.7 ft/s).