Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 22 Forming Systems

FORMING SYSTEMS

FORMWORK Formwork accounts for 30 to 70% of the construction cost for concrete framed buildings, hence its importance as a major component of the equipment array used on such construction projects.

FORMWORK The selection and use of forming systems are inseparable from the selection and operation of the on-site cranes and other lifting and concrete-placing equipment. Forming systems—for slabs, walls, columns, and other repetitious concrete elements of the structure—are designed and fabricated for many reuses.

FORMWORK The constructor’s project engineer is extensively involved with various planning aspects of their selection, ordering, erection, stripping, and reuse. Construction companies procure forming systems by either direct purchase or short-term rentals.

FORMWORK The labor cost associated with any selected system is an essential part of the economic calculations and comparison of forming alternatives

FORMWORK CLASSIFICATION Conventional formwork –assembled in situ from standard elements new for each use and is disassembled after each use

FORMWORK CLASSIFICATION Industrialized formwork –mostly factory-fabricated products and are used many times as one unit without being disassembled and assembled again for each use

FORMWORK AND THE PROJECT ENGINEER Close interrelationship between project engineering, site management, and the formwork supplier on the new Parliament House project in Berlin, Germany

FORMWORK DESIGN Vertical loads on horizontal forms Dead loads Live loads

FORMWORK DESIGN Lateral pressure of concrete on vertical forms Horizontal pressure on the surface of the forms, proportional to the density and depth of the concrete in a liquid or semiliquid state

LATERAL PRESSURE OF CONCRETE ON VERTICAL FORMS Figure (a) shows a full liquid head pressure

LATERAL PRESSURE OF CONCRETE ON VERTICAL FORMS Figure (b) shows a situation where the concrete began to harden, thus exerting a pressure at the lower part of the form that is less than the full liquid head pressure (depth of fluid concrete from top of placement is h 1 )

Figure (c) shows a situation similar to Fig. (b), but with a lower rate of filling the forms; this results in yet a lower maximum pressure and a smaller height of liquid head pressure, h 2 < h 1 LATERAL PRESSURE OF CONCRETE ON VERTICAL FORMS

FORMWORK: A LAYERED SYSTEM (horizontal)

Stringers Joist Shores

FORMWORK: A LAYERED SYSTEM (vertical)

Strongback Wale Brace/stabilizer Ties Studs Brace/stabilizer Large custom- made wall forms with timber studs and steel wales and strongbacks FORMWORK: A LAYERED SYSTEM (vertical)

MATERIAL COST L n = salvage value after n years USCRF = unified series capital recovery factor

REPAIR & MAINTENANCE USSFF = unified series sinking fund factor

MODIFICATION COST PWCAF = present worth compound amount factor

LABOR COST

EXAMPLE Construction company considers the purchase of a set of half-tunnel forms for $20/sf. The forms are to be used 200 times for the forming of 1,000 sf of walls and 1,000 sf of slabs per use on a series of residential buildings over a period of 4 yr, and then they will be sold.

EXAMPLE Salvage value is expected to be 10% of original purchase price. No maintenance costs are expected. Labor productivity is estimated at labor hr/sf. Hourly wages are $22. Consider 5% annual interest rate. What is the average formwork cost (material and labor) per use for this project?

EXAMPLE Actual area of forms: (1,000 sf slab + 2 × 1,000 sf wall) × 1.15 = 3,450 sf Note that for every 1 sf of wall, 2 sf of forms, both sides of the wall, are required

EXAMPLE Purchase price: 3,450 sf × $20/sf = $69,000 Average number of uses per year: 200/4 = 50 Salvage value: $69,000 × 10% = $6,900

EXAMPLE Material cost per use: Labor cost per sf:

EXAMPLE Labor cost per use: Formwork cost per use: material maintenance labor

VERTICAL SYSTEMS Vertical formwork is designed based on a rate of placement and the resulting lateral pressure curve—the pressure of liquid concrete and timing of initial set.

WALL FORMS Ganged forms

WALL FORMS Steel large- panel wall forms

WALL FORMS Large custom-made wall forms

WALL FORMS Wall form system including main work platform, upper concreting platform, and finishing trailing platform

WALL FORMS Single-sided wall forming system

Self-climbing forms in high-rise construction of the Park Tower in Chicago WALL FORMS

Custom-made forms for small series of columns COLUMN FORMS Site-fabricated timber forms

COLUMN FORMS Custom-made forms for small series of columns Site-fabricated steel forms

Custom-made forms for large series of columns COLUMN FORMS Factory- fabricated steel forms

HORIZONTAL SYSTEMS Typically come in two configurations: –hand-set forms –table (flying) forms –column mounted forms (also termed “drawer” forms) Stripping times much longer than for vertical elements

PLYWOOD-AND-ALUMINUM HAND-SET SLAB FORMS With drophead system

DROPHEAD SYSTEM FOR HAND- SET SLAB- FORM

Table on screw-jacks ALUMINUM TABLE FORM (TRUSS SYSTEM) SUPPORTED ON JACKS

Lowered table

Lifted by a crane using a c-frame TABLE FORM

Being removed by a crane located near the facade of the building

Tables with extension spandrel beam forming and working deck chained to the floor to withstand overturning

COMBINED VERTICAL & HORIZONTAL SYSTEMS Wall-and-slab forming systems come in two configurations: –half-tunnel forms –full-tunnel forms (not to be confused with forming systems for tunnels) Both are commonly referred to as tunnel forms, or simply tunnels

Cellular-type building suitable for using tunnel forms TUNNEL FORMS

HALF- TUNNEL FORMS

Two tunnel form halves are connected to create a full unit form TUNNEL FORMS

Hydraulic contraction of a full tunnel form for stripping TUNNEL FORMS

Inside view of a tunnel form with hydraulic knee struts and heating blowers

Hotel construction FULL-TUNNEL FORMS

SHORING TOWERS Formwork for cast-in-place concrete in high-clearance construction is commonly based on multitier shoring towers, also termed load towers or support towers

Family A Family B

Family AFamily B

Family CFamily D

Form support using 240-ft-high aluminum shoring towers with carrying capacity of 18,000 lb/leg

TRAVELING FORM SYSTEM FOR A TRAIN TUNNEL

SAFETY The mechanical handling of formwork on site, a characteristic of industrialized forming systems, is a critical operation All parties involved in crane handling of the form should be aware of form’s weight and the proper handling method