The special sessions will focus on advances in the serviceability of concrete bridges and structures. Of interest are presentations concerning a wide variety of technical aspects from laboratory experiments to field applications. Specific subjects include the prediction of deflections in reinforced and prestressed concrete members, cracking problems and mitigation methodologies, state-of-the-art evaluation techniques, strategies to achieve the concept of serviceability-based design and construction, and practical approaches that can assist engineering professionals in retaining serviceability requirements.
Learning Objectives:
(1) Learn the recent advances in research with regard to serviceability;
(2) Comprehend assessment methodologies for constructed concrete structures;
(3) Recognize emerging concepts in the area of serviceability-based design;
(4) Learn how laboratory research is translated into practice.
Serviceability of Concrete Structures for Explosives Operations Locations
Presented By: Michael Pickett
Affiliation: US Army Corps of Engineers
Description: This paper presents a structural health and visual inspection technique developed by the U.S. Army Corps of Engineers (USACE) Facilities Explosives Safety Mandatory Center of Expertise (FES MCX) and the Engineering Research and Development Center (ERDC) Geotechnical and Structures Laboratory (GSL) for the inspection of reinforced concrete Explosives Operations Location (EOL) facilities. This inspection process has been utilized to inspect over 1000 structures across multiple countries over the last decade and aid Department of Defense (DoD) installations in planning and budgeting for concrete repairs. This process has also been modified for use in live-fire training operations in concrete facilities and coupled with analyses to determine facility adequacy for explosives operations with desired charge weights, based on the given facility’s current structural health rating and its analyzed ability to remain elastic during repeated intentional detonations. The FES MCX partners with (ERDC) for concrete coring and testing of samples to determine the estimated remaining service life of concrete structures based on the carbonation front of cored samples determined by the carbonation tests in relationship to the steel reinforcement. Examples of historical application will be given, and details provided on how these methods can lead to improved lifecycle cost for concrete structures and paired with design development criteria for optimal results.
Simplified Method for Serviceability Design of Cracked Prestressed Concrete Members Belonging to Class C Section
Presented By: Deuck Hang Lee
Affiliation: Chungbuk National University
Description: In current ACI 318 code, crack control design criterion for prestressed concrete (PSC) members is stricter than conventional reinforced concrete (RC) members. In particular, it is stipulated that the net tensile stress of prestressing strands should be controlled under 250 MPa in the serviceability design of PSC members belonging to the Class C section that is expected to be cracked under service load conditions. To this end, the nonlinear cracked section analysis is essentially required to estimate the tensile stress of the prestressing strands under the service loads, which requires cumbersome iterative calculations in practice. This study aims at presenting simplified method to estimate the net tensile stress of the prestressing strands (?fps) under the service load conditions and also tabulated checking method whether the net tensile stress (?fps) exceeds the stress limit with respect to the magnitude of effective prestress (?fps). Finally, applicability of 2,400 MPa Grade strands is also experimentally investigated.
Stress Measurement of Reinforcing Bars Embedded in Concrete by Hole-drilling Method
Presented By: Mohammad Nikoukalam
Affiliation: Simpson Gumpertz & Heger
Description: This research examines the hole-drilling method per ASTM E837, known for its minimal invasiveness, for measuring in situ stress in reinforcing bars embedded within concrete structures. The primary objective is to ascertain the applicability of this method in estimating non-apparent stresses, such as those resulting from the external loads, creep, shrinkage, or alkali-silica reaction, that are needed for structural assessment. Systematic experiments on reinforced concrete beams are conducted to validate the method’s viability in identifying these critical in situ stresses. The findings highlight the potential of the hole-drilling method to enhance structural health monitoring practices, offering an accurate tool for assessing stress states crucial for the maintenance and safety of concrete structures. This study contributes to the field by confirming the limits and applicability of the ASTM E837 standard for estimating the existing stress in the embedded reinforcing bars.
Vibration Performance of Dry and Half-Wet Steel Composite Floors for Modular Buildings
Presented By: Tae-Sung Eom
Affiliation: Dankook University
Description: After the Covid-19 pandemic, modular construction has been attracting attention in Korea as a promising solution to reduce construction time and labor demand. In this study, a new dry and half-wet composite floor system for modular homes was investigated with an emphasis on vibration performance under service loading. The composite floors of 2 m wide and 6 m long, consisting of precast concrete panels, steel beams and cast-in-place mortar topping, were fabricated. Ultra-high performance concrete connectors were used to facilitate the assemblage of the perimeter steel beam frame, the main structural element carrying gravity loads. To improve vibration performance, the steel beams of adjacent modular units were connected by bolting and such intermodule connection details were considered as the main test parameter. The vibration periods and acceleration responses of the composite floors were measured from laboratory tests such as impact, heel drop and walking loads. The vibration characteristics of the composite floors were investigated further through finite element analysis. The measured and predicted vibration performances were compared with the acceptance criteria in AISC Design Guide 11.
Effects of Evolving Vehicle Loading on the Serviceability of Concrete Bridges
Presented By: Andrew Foden
Affiliation: HNTB
Description: Various vehicle loadings are considered and their effects on the service performance of concrete bridges are investigated.
Evaluation of Serviceability and Safety of Slabs in Wall-type Residential Building Under Construction
Presented By: Hyeon-Jong Hwang
Affiliation: Konkuk University
Description: During construction, construction load on slabs can be up to 2 to 3 times their self-weight, which can damage serviceability and structural safety of the slabs with early-age concrete. In the present study, an existing model to predict the load on slabs during construction was modified to properly predict construction load when using aluminum formwork and shores and incorporating reshoring practices. A safety assessment model was devised to predict the failure probability of slabs for cracking, flexure, and shear, by considering measured construction load and construction error of placement of longitudinal reinforcement. To verify the accuracy of the modified model and apply the safety assessment model, loads on shores were measured at a wall-type residential building under construction in South Korea. For 4 stories, the loads on shores and distribution of cover thickness of slabs were measured and the measurement lasted for 58 days. The comparison between the predicted and measured slab construction loads showed that the predicted construction load agreed with the measured construction load. The result of safety assessment of the building showed significantly low failure probability of the slabs.