February 1990 Table of Contents

Features Practical Shear Reinforcement for Concrete Flat Slabs

The thickness of most long-span flat slabs, two-way slabs without beams, is controlled by the shear strength of the concrete slab surrounding the supporting column. The shear resistance of these slabs can be increased by means of shear reinforcement. If the shear resistance is increased, slab thickness can be decreased resulting in less concrete materials and lower structure deadweight, reducing costs. But installing typical shear reinforcement, shear heads, and stirrup cages is difficult and costly. To take advantage of the reduced slab thickness and decreased cost that shear reinforcement could provide, a more efficient shear reinforcement has been developed. Read more

Features How to Get Paid in Full and on Time

Few industries place as much product in the hands of buyers as far in advance of payment as the construction industry. Late payment is the accepted norm for construction contractors. What's surprising is the blase attitude contractors take toward the payment system. This attitude, along with the system itself, compounds the payment problem for contractors. In the language of most contracts and in the role of most designers, there's an assumption that contractors don't do the work without a gun held to their heads. This creates mistrust. Contractors often feel they have little power to get paid and that entitlement to their money is clouded. They send in their payment requisition, and if the architect disagrees, it's returned with red-lined changes. Then the contractor retypes it, signs it, and sends it to the architect again. This puts the contractor in the passive role of taking what they can get, rather than invoicing customers for services rendered. Changing your payment requisition is saying that you were wrong in the first place. Read more

Features Self-Lifting Forms Shape Building Cores

Attendees at World of Concrete 90 were shown a fast and efficient method of constructing the concrete core of high-rise building. The technique is to make the forms self-lifting by building a system including jacks to raise the forms without crane assistance. The core form consists of a two-way grid of intersecting steel beams that support a work deck and safety railings on top. Gang form panels made with aluminum framing members and three-quarter-inch plywood face hang from the grid, as do the hydraulic rams that move the system up the building. Inside the building core, the work platform is suspended at the proper elevation for workers to release form support brackets. Read more

Features Flatwork Forming Is a Snap Using Plastic Formwork System

A plastic forming system designed to save form erection and stripping time needs no nailing, double staking, or form release agents for assembly. Its basic components include 2x4- or 2x6-inch forms, end connectors, and cam lock clamps. The hollow forms are about one-third the weight of wood. Molded plastic connectors stapled into the ends of each form allow workers to snap forms together for setup and unsnap them when stripping. Each form has a dovetail slot that runs the entire length of one side. Reusable cam lock clamps can be inserted anywhere along the slot to coincide with stake locations, even after the form is in place. Read more

Features Hydraulic Cutter Strips Pile Heads in Minutes

Using jackhammers to strip heads of foundation piles is a time-consuming process that can take an hour or more for each pile. Now there is an alternative to the jackhammer that's quicker, easier, and more economical: a hydraulic pile cutting machine that can strip a pile head and carry away the cutting debris to a dump truck in just 3 to 5 minutes. Read more

Features Water-Source Heat Pump Economically Controls Concrete Temperature

While searching for a way to cool concrete and still make a profit, Hodgson Concrete Company of Montgomery, Alabama learned about a water-source pump that controls batch water temperature to either cool or heat concrete. Read more

Features Design for Constructability: a Contractor's View

Designing and building economical structures requires knowing the difference between design decisions that really improve efficiency and those that only appear to. Here are some suggestions for improving constructability, lowering costs, and improving the quality of the structure: Read more

Problem Clinic Will Calcium Chloride Thaw a Frozen Subgrade?

We're supplying ready mixed concrete for a floor slab that will be placed in freezing weather. We warned the contractor about placing concrete on a frozen subgrade. He says he'll throw flake calcium chloride on the subgrade surface to thaw it before he pl Read more

Problem Clinic Epoxy Specifications for Crack Injection

We're bidding on a crack injection job where the requirements for the injection epoxy resin are specified. The specs require a compressive strength of 15,000 psi, tensile strength of 8000 psi, and slant shear strength of 5000 psi. We're having trouble fin Read more

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