MAGAZINE - Concrete International

ir_71 · 10-07-2017, 06:00 AM

Proposals for New One-Way Shear Equations for the 318 Building Code
The basic one-way shear provisions in the ACI 318 Building Code have remained unchanged since 1963. However, researchers have developed new methods that better account for the depth of the compression zone, the amount of longitudinal reinforcement, and the size effect on shear capacity. This article introduces a set of six articles that describe proposals being used to develop change proposals for the one-way shear equations for the ACI 318-19 Code. The impetus and activities leading to the change proposals are summarized.

Concrete Quality Technical Manager Certification
ACI is offering a new certification program—Concrete Quality Technical Manager (CQTM). The CQTM program is intended to identify and confirm individuals who possess the knowledge and experience necessary to supervise an effective concrete quality assurance/quality control program, manage those duties on behalf of a ready mixed concrete company, or represent the design professional in technical matters pertaining to the concrete used on a project.

Updating the ACI Shear Design Provisions
Shear provisions in ACI 318-14 Code have a few disadvantages that could be improved. For example, the provisions can provide overly conservative designs for members heavily loaded in shear and unconservative designs for deep one-way slabs without stirrups. The Code also contains eight separate equations to calculate the nominal shear strength provided by concrete. This article focuses on a method, based on first principles, to simplify shear provisions in the Code and address safety issues.

One-Way Shear Design Method Based on a Multi-Action Model
Shear strength of a reinforced or prestressed concrete beam results from the interaction of different resisting actions. The model described in the article is a simplification of the multi-action shear model developed by the authors. Presented equations were simplified for submission to ACI-ASCE Joint Committee 445, Shear and Torsion, considering distinct features of the ACI 318-14 Code with respect to European engineering practice.

A Unified Approach to Shear Design
Shear design expressions in ACI 318-14 have limitations related primarily to beams with low percentages of flexural reinforcement, beams with high-strength concrete, and member size. Also, different design approaches are required for nonprestressed and prestressed members. This article shows that it is possible to eliminate these limitations, unify design methods, and provide for improved safety of concrete structures.

Shear Strength of Prestressed and Nonprestressed Concrete Beams
ACI 318-14 requirements for determining the shear strength of concrete beams are separated into two distinctly different methods—one for prestressed concrete (PC) and one for nonprestressed reinforced concrete (RC). To simplify the shear strength calculations, a shear prediction equation incorporating a factor known as the “arch action factor” is proposed. This factor provides a means to unify flexural shear failure and web shear failure, and it has been shown to be applicable to both PC and RC.

Unified Shear Design Method of Concrete Beams Based on Compression Zone Failure Mechanism
Park, H.-G., and Choi, K.-K., Concrete International, V. 39, No. 9, September 2017, pp. The ACI 318-14 Code specifies the use of 14 equations for evaluating one-way shear strength. These detailed equations are inconvenient to use and need to be revised and combined into a unified method. This article presents a shear strength model based on the concrete compression zone failure mechanism. The shear strength of the compression zone is defined by a material failure criterion considering the effect of the compressive normal stress developed by flexural moment.

Proposal for ACI 318 Shear Design
Shear design should not be regarded as a sectional design process (designers check that the applied shear force does not exceed the shear capacity in vertical sections of a beam). Instead, the design process should look at load transfer in the whole member. This is best done by using strut-and-tie models. In this article, truss models, valid for members with shear reinforcement as well as without, are described. The models are shown to provide very good agreement with test results.

Embracing a Culture of Documentation

ACI Sponsors 30th Annual National Concrete Canoe Competition
ACI traveled to the Colorado School of Mines in Golden, CO, June 17-19, 2017, to connect with students, faculty advisors, and young professionals at the 30th Annual National Concrete Canoe Competition.

Notable Concrete in Anaheim

Concrete Q&A: Modification of Existing Structure with Change in Loads
The Q&A in the May 2017 CI featured an interesting question about existing structures. The answer is related to one of my current projects. I am the licensed design professional (LDP) responsible for the structural design of a modification of a hotel building at a ski resort. The owner wants to create an exterior rooftop terrace (bar) on the top floor of the building by removing a portion of the existing roof and façade. The original floor was designed for hotel occupancy. However, the new terrace area would be exposed to both snow loads and a higher occupancy floor load. The existing structure is reinforced concrete beam and slab construction from the early 1980s. What are the appropriate code provisions for the evaluation of the existing structure? How should I deal with the snow load (including drifting snow) and increased live load on the new terrace area (again, the structure was designed for residential floor loads)?

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ir_71 · 10-08-2017, 06:56 AM

Precast Concrete Pavement Innovations
Precast concrete pavements (PCPs) have been shown to be promising alternatives for repair and rehabilitation of the aging highway infrastructure in the United States. The article presents details on technical considerations related to design, fabrication, and installation of PCPs, especially concrete requirements, joint spacing, support conditions, load transfer at joints, panel reinforcement and prestressing, and panel production and installation rates.

Banding Together to Reach Out
To create a perimeter band of free-flowing workspaces with maximal views of the surrounding landscape at the Novartis Oncology Research Building in East Hanover, NJ, the designers significantly set back the columns from the façade, resulting in long-span cantilevers and large, column-free expanses. The challenges with the quantity and density of a bonded post-tensioning system necessary to meet performance requirements could only be met through open, creative, and precise collaborative efforts between the owner, builders, manufacturers, installers, and designers.

Integrating Precast Cladding and Structure
In regions with high seismic risk, a precast hybrid moment frame (PHMF) is an optimum system for combining cladding and structure. The PHMF comprises high-quality precast column and beam elements, produced under factory-controlled conditions, that are connected using traditional construction methods and materials. The system is self-righting—the elastic, unbonded post-tensioning is designed to overcome yielding in the frame and pull the building back to a righted position.

Analysis and Design of Double-T Flanges
Pretensioned concrete double-T members are widely used as floors in parking garages. Uniformly distributed live load usually governs pretensioned design of the member in the main span direction, and the concentrated load usually governs the design of the overhanging outer flanges of the slab portion of the member. The article compares flange moments determined using elastic plate theory, various assumptions following the approaches given in the PCI Design Handbooks, yield-line theory, and consideration of the loadings suggested by Malik.

Post-Tensioning Institute 2017 Project Awards
The Post-Tensioning Institute (PTI) announced its 2017 Project Awards during the 2017 PTI Convention Awards Dinner in Atlanta, GA, in May.

ACI Chapters are Pivotal to ACI’s Mission
ACI's 93rd President, Michael J. Schneider, summarizes his 2016 and 2017 visits to multiple ACI Chapters, as a fulfillment of his mission to strengthen the relationship between ACI National and the local chapters. During those visits, he met many dedicated people interested in helping ACI fulfill its mission and vision. He also observed that the best ACI Chapters have members from all areas of the concrete industry and provide programs that are of interest to these various segments.

ACI Student Chapter Activities
Eastern Pennsylvania and Delaware Chapter – ACI Hosts Student Beam Competition, USFQ Student Chapter – ACI Visits Subway Project in Ecuador, AASTMT Student Chapter – ACI FRC Bowling Ball Competition, FIU Student Chapter – ACI Teams Place in Concrete Bowling Ball Competition, Kansas Chapter – ACI Awards $6000 in Scholarships, Maryland and National Capital Chapters – ACI Award $55,0000 in Scholarships, Nebraska Chapter – ACI 2017 Richard T. DeLorm Scholarships, 2017 ACI Student Concrete Cylinder Competition in Qatar, Universidad de Sonora Student Chapter – ACI Concrete Plant Tour, Université Laval Student Chapter – ACI Conference on Concrete Expertise, Recent Award-Winning Student Chapters.

Recent ACI Chapter Awards and Achievements
Nebraska Chapter – ACI Awards of Excellence, Eastern New York Chapter – ACI Celebrates 50 Years, Rocky Mountain Chapter – ACI Excellence in Concrete Awards, San Diego International Chapter – ACI Looks Back on 50 Years.

ACI Chapter Directory

Dangers of Silica Dust
Inhalation of "respirable crystalline silica" (particles size less than 5 micron [0.2 mil]) can result in silicosis and lung cancer. These small dust particles can be created by chipping, drilling, grinding, diamond polishing, and sawing materials containing crystalline silica, such as concrete and stone. The new OSHA regulations regarding silica exposure for construction that went into effect on September 23, 2017, and their implementation by tool manufacturers, are discussed.

Concrete Q&A: Acceptance Testing Requirements in ACI Standards
Q. The last paragraph in the August 2017 Q&A states that ASTM C31/C31M1 allows only standard-cured specimens to be used for acceptance testing for specified strength. Could you expand on that? What do ACI documents state?

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ir_71

Position Statements from the Concrete Polishing Council of ASCC
Concrete Polishing Association of America (CPAA), created by a small group of contractors in 2010, is now the Concrete Polishing Council (CPC)—one of four specialty councils within American Society of Concrete Contractors (ASCC). The CPC has spent the last year developing educational products, refining its certification process, and publishing documents to help define the industry and the polishing contractor’s place in it. Three Position Statements that accompany this article comprise some of this work.

Uncoupling Modulus of Elasticity and Strength
To limit lateral deformations and ensure occupant comfort, designers of tall concrete buildings may specify a high modulus of elasticity (MOE) for the structural concrete. While MOE can be raised by increasing concrete compressive strength or using stiffer aggregates, such mixtures can be prone to brittle behavior and high autogenous shrinkage. There is an alternative way to obtain a high MOE, using carbon nanotubes, which, if well dispersed, can increase MOE of concrete without increasing the compressive strength.

Winners of the 2017 ACI Excellence in Concrete Construction Awards
A house comprised of architectural concrete, R·torso·C, received “The Excellence Award,” the highest honor in the ACI Excellence in Concrete Construction Awards program for 2017. The winning project was submitted by the Japan Concrete Institute. This award is given to a project that demonstrates excellence in concrete innovation and technology and stands out above all other entries. Eleven additional global projects were recognized October 16, 2017, during the Gala event at The ACI Concrete Convention and Exposition in Anaheim, CA.

Can We Design Concrete to Survive Nuclear Environments?
This article is a summary of a panel discussion that took place during the 123 Forum session at The Fall 2016 ACI Concrete Convention and Exposition in Philadelphia, PA. The panelists and one of the moderators have been actively involved in research efforts to improve understanding of the effects of nuclear environments on concrete and cementitious grouts as well as the ability to monitor degradation of nuclear structures.

A Tale of Two Dams
The failure of the primary service spillway for California’s Oroville Dam on the Feather River has piqued the interest of the dam building profession worldwide. Possible origins of the failure are examined through a comparison between Oroville Dam and Daniel-Johnson Dam in Quebec, Canada.

Concrete Q&A: Welded Wire Reinforcement Placement
ACI 301-16 provides placement requirements for WWR

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ir_71 · 12-08-2017, 05:15 AM

Dispersion of Fibers in Ultra-High-Performance Concrete
Fiber balling is a challenge in scale-up production of ultra-high-performance concrete (UHPC) using conventional concrete mixing practices. Therefore, many producers resort to the use of specialty mixers, and this increases the cost of UHPC. This article presents an investigation into resolving fiber balling issues by adjusting the types, shapes, and sizes of fibers in the mixtures.

Titanium Finds a Home in Civil Engineering
The Oregon Department of Transportation has completed a bridge rehabilitation project using titanium bars. Girders on three of the four bridge spans of an overpass near Mosier, OR, were strengthened using a total of 70 titanium near surface mounted bars, a solution based on research conducted at Oregon State University. In addition to high tensile strength, ductility, and environmental durability, titanium offers high shear strength and resistance to mechanical damage, high maximum service temperature, and thermal expansion compatibility with concrete.

Concrete Product & Service Guide

Company Directory

2018 ACI Honors and Awards Program
The American Concrete Institute showcases the contributions and efforts of its global membership and the concrete industry worldwide through its varied honors and awards program. ACI is seeking nominations for the 2018 award cycle.

ACI Officer Nominations for 2018-2019

LafargeHolcim Awards 2017 North America

The Strength of Circles
Tokyo-based design firm nendo created a new plaza, called CoFuFun, in the small town of Tenri, Nara, Japan. The plaza features five discs, placed at four different heights, each with concentric stairs that also act as benches and amphitheater seating. The precast manufacturer created the discs by casting precast concrete pieces as giant pizza slices. Each disc comprises up to 37 different pieces (slices).

The Challenges of Achieving Compatibility in Concrete Repair
The issue of compatibility in engineered repair composite systems is usually ignored or misinterpreted by design engineers, often due to a lack of knowledge and/or misleading guidance. The authors discuss some of the critical issues concerning the achievement of compatibility in a concrete repair composite system and its influence on repair durability. They also point out important gaps in the industry’s basic knowledge of the subject.

Concrete Q&A: Rebound Hammer and In-Place Strength Testing; Tolerances for Concrete Slabs Supporting Steel Tanks
Q. According to Provision 1.6.4.2 of ACI 301-16,1 a rebound hammer cannot be used for in-place strength testing. Does ACI recommend any other nondestructive testing (NDT) method for in-place strength evaluation? Q. My company will be placing a concrete slab foundation designed to directly support the base of a steel tank. Does ACI have any documents that discuss tolerances for elevation of such slabs after placement?

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ir_71 · 01-06-2018, 05:38 PM

Racing Towards a Green Future
The Great Northern Concrete Toboggan Race is a competition among engineering students from colleges and universities across Canada and the United States. In 2017, the Queen’s University, Kingston, ON, team won the overall championship as well as the award for Most Sustainable Toboggan with the self-consolidating magnesium silicate concrete racing toboggan.

Field Application of Nonproprietary Ultra-High-Performance Concrete
Researchers at the University of Michigan, Ann Arbor, MI, developed nonproprietary ultra-high-performance concrete (UHPC) mixtures that can be made from off-the-shelf products and do not require onerous placement or special curing processes. The resulting material has similar performance characteristics but is substantially less expensive than proprietary UHPC mixtures.

The Rheology of Control Flow Concrete
A new family of polycarboxylate polymer admixtures enables the production of control flow concrete. Control flow concrete is produced using mixture proportions typical of conventional concrete. While it has the same segregation resistance as conventional concrete, it flows more readily and has high passing ability through congested reinforcement.

2017 Concrete Society Awards for Excellence in Concrete
The 2017 Concrete Society Awards for Excellence in Concrete were presented in London, UK. The 2017 Winner was the Queensferry Crossing, Forth Replacement Crossing, Rosyth, Scotland, the world’s longest three-tower cable-stayed bridge. Five other projects were also recognized as Highly Commended.

Concrete Q&A: Epoxy-Coated Reinforcement and Cover Depth Against Ground

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ir_71 · 02-11-2018, 12:09 PM

RCC Dam Construction
Key features of roller-compacted concrete (RCC) dams are highlighted, using various dam types as examples. Topics include lift interfaces, facing systems, spillways, intakes and outlets, internal galleries, and joints. Test sections are recommended for training and to demonstrate that the systems, methods, and equipment proposed for a project will meet project specifications.

ACI Concrete Sustainability Forum Celebrates 10 Years
ACI Concrete Sustainability Forum X was held in 2017 at The ACI Concrete Convention and Exposition in Anaheim, CA. The Forum featured presentations from eight speakers, including the presidents of both ACI and fib. Presented topics included sustainability activities within ACI, fib, and ISO, new technologies for sustainability, and actions for the next decade.

ACPA 2017 Excellence in Concrete Pavements Awards
The American Concrete Pavement Association (ACPA) named the recipients of its 28th Annual “Excellence in Concrete Pavements” awards, recognizing quality concrete pavements and honoring the associated contractors, engineers, and project owners. Gold and silver level awards were given to 29 projects constructed in 2016 in the United States and Canada. Gold level awards are summarized in this issue.

Three-Sided High-Rise in Mexico City
Torre Reforma, a 57-story mixed-use building, is a new addition to the skyline of Mexico City, Mexico. The building is triangular in plan with elevators and egress stairways contained in the apex of the triangle and long-span pyramidal floor trusses. The trusses conceal plumbing, electrical, and mechanical systems, and allow for maximum ceiling heights and a column-free interior, facilitating unobstructed views over the city from every-level.

Making Connections and Setting an Attendance Record
A record number of 2235 attendees participated at The ACI Concrete Convention and Exposition – Fall 2017, held in Anaheim, CA, October 15-19, 2017.

Concrete Q&A: Chloride Concentration in Soil and Exposure Classes, and Cleaning Slabs During Tilt-up Construction
I’m designing a structure that will be exposed to chlorides in soil, so I’m reviewing the requirements listed in Table 19.3.2.1 —Requirements for concrete by exposure class, in ACI 318- 14.1 The chloride concentration in the soil is lower than the concentration in seawater, so can I specify concrete with a strength value between 2500 and 5000 psi (17.2 and 34.5 MPa), based on C1 and C2 exposure classes, respectively? Does ACI provide recommendations on cleaning concrete slabs during tilt-up construction?

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ir_71 · 04-03-2018, 04:06 PM

Naked Concrete
Reston Station OB1, Reston, VA, is a striking 16-story office tower showcasing a unique lateral force-resisting system comprising a diagonalized, exposed concrete exoskeleton. The concrete exoskeleton columns are aesthetic features that support gravity loads and resist lateral loads in the north-south direction. Six shearwalls, located in the core of the building along the elevator and stair shafts, serve as the lateral force-resisting system in the east-west direction. Key design features are summarized.

Butterfly House
The Butterfly House, a residence in Monterey County, CA, provides unobstructed views of the surrounding environment and wildlife. The house is formed by exposed concrete walls and floors, operable glass walls, and folded roofs inspired by butterfly wings. The central pavilion houses the main living, dining, and cooking spaces, while the two other pavilions provide spaces for sleeping, bathing, and relaxing.

Notable Concrete in Salt Lake City
Several projects near The Concrete Convention and Exposition at the Grand America and Little America Hotel, in Salt Lake City, UT, are presented. Some of the projects include Salt Lake City Public Safety Building, George S. and Dolores Dore Eccles Theater, 111 S. Main Street, City Creek Building, Gateway Block B, Jordan River Pedestrian Bridge and Trail, Artesian Springs Tower, Living Planet Aquarium, Mountain “S” Home, and The Void.

2018 Decorative Concrete Council Award Winners
The Decorative Concrete Council, a specialty council of the American Society of Concrete Contractors, announced the winners of its tenth annual Decorative Concrete Awards competition. The winners were recognized at a ceremony at World of Concrete, Las Vegas, NV. T.B. Penick & Sons, San Diego, CA, won the WOW! Award, best overall project, for the Atlanta Botanical Garden, Atlanta, GA.

2017 Scofield Decorative Concrete Awards
Scofield, a business unit of Sika Corporation, announced the winners of its 10th Annual Decorative Concrete Awards contest. The annual contest is free to enter, and is open to any contractor who uses Scofield Systems in the entered project. The awards ceremony was attended by about 85 contractors, media members, and others.

ACI’s New Fellows
ACI will recognize 24 members who have been honored with the rank of Fellow of the American Concrete Institute (FACI) at The ACI Concrete Convention and Exposition in Salt Lake City, UT.

Concrete Q&A: Acceptable Concrete Cracking
What is considered as acceptable concrete cracking in cast-in-place foundation walls and slabs per ACI documents? My company is the concrete contractor on a large warehouse project, and I want to discuss the potential for cracking with the contractor and the owner.

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