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FORMWORK DISASTERS We are reviewing Chapt. 1&2 and we assigned Chapt. 3 & 4 for reading assignment!!! Chapter One- Introduction to Forming Chapter Two-

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Presentation on theme: "FORMWORK DISASTERS We are reviewing Chapt. 1&2 and we assigned Chapt. 3 & 4 for reading assignment!!! Chapter One- Introduction to Forming Chapter Two-"— Presentation transcript:

1 FORMWORK DISASTERS We are reviewing Chapt. 1&2 and we assigned Chapt. 3 & 4 for reading assignment!!! Chapter One- Introduction to Forming Chapter Two- General Objectives in Formwork Building Chapter Three-Overall Planning for Formwork Chapter Four-Materials, Accessories, Proprietary Products CHAPTER 2

2 What is forming and formwork? What is its purpose? What are the objectives of any form design? The form design must provide, THE BEST QUALITY SAFETY ECONOMICS What kind of nomenclature or terminology is associated with forming? Discussion of some Case Studies on Pages 2-4 to 2-8 FORMWORK COST AND CONSIDERATIONS

3 New York Coliseum FORMWORK DISASTERS Concrete was placed on the Main Exhibition Floor of the New York Coliseum Forms for the floor slab were being supported on two tiers of shores Bottom shores were wood 4x4s, capped with horizontal 4x4s and cross –braced horizontally. Adjustable metal shores were placed directly over the 4x4 posts to form the second tier There was little diagonal cross-bracing or horizontal bracing on the adjustable shores. At the time of the collapse there were eight or nine motorized buggies transporting concrete to the area A horizontal thrust developed through the combined effect of the movement and sudden stopping of the buggies

4 New York Coliseum where rapid deliveries of power buggies introduced lateral forces FORMWORK DISASTERS New York Coliseum

5 Increased diagonal bracing was added to all remaining shoring for the New York Coliseum following partial collapse of formwork FORMWORK DISASTERS New York Coliseum

6 Bailey’s Crossroads in Virginia 14 workers were killed FORMWORK DISASTERS Flat plate apartment building had 26 stories plus penthouse and four –story basement Columns were normal weight concrete, and slabs were lightweight concrete, 8 in thick. One floor was cast per week. Forms were supported by floor 7 days old or older, which in turn was propped to a floor 14 days old or older. 24 th Floor was being cast when collapse occurred. 24 th Floor was shored to the 23 rd Floor which was only about 5 days old. Workmen began knocking out the shores supporting that 5 day old floor (the 23 rd ), even though 2 full floors of shoring was required in the design The overloaded 23 rd floor failed in shear around one or more columns, triggering a collapse throughout the bldg.

7 Bailey’s Crossroads in Virginia 14 workers were killed FORMWORK DISASTERS

8 More Accidents in Forming FORMWORK SAFELY 15 injuries and one death Contractor taking risk for economic reasons

9 Preventive Measures FORMWORK SAFELY High Shoring with a heavy load at the top is vulnerable to eccentric or lateral loadings. Diagonal bracing improves the stability of such a structure, as do guys or struts to solid ground or completed structure

10 SHORES AND RESHORES Read Chapt. 5 Chapter Five- Loads and Pressures Book Overview

11 What are the loads experienced in formwork? Vertical Dead Load Weight of reinforced concrete (DL) Average unit weight of concrete is considered 150 pcf (includingrebar) For slabs we use 12.5 #/sq ft.per one inch of slab thickness Vertical Live Load Weight of material, workmen, and equipment (LL) minimum LL is 50 psf (includes workmen, runways, screeds, & equip. minimum LL is 75 psf when motorized carts are used

12 What are the loads experienced in formwork? Vertical Live Load & Dead Load Regardless of slab thickness, minimum DL+LL is 100psf, and 125psf if motorized carts Forms and shores must be joined securely and attached to base support to insure against uplift loads (see p. 5-3)

13 How do shores and reshores function within our design? Shores and Reshores shores that support freshly placed concrete may be supported by floors that are exceeding there full design strength, therefore shores must be developed in as many floors as can support the capacity 10 considerations for shoring are mentioned on p. 5-3

14 How do shores and reshores function within our design? Reshores Reshores replace shores after stripping The sequence is as follows Set up forms and shores for new concrete remove reshores at lowest floors and forms and shores from next level above replace reshores snugly under the slab just stripped, but without reshores carrying any load when they are first placed

15 How do shores and reshores function within our design? Reshores and Shoring Sample problem review assumptions for hand calculation review table 5-2

16 Wooden ReShores from Text 4-68

17 Adjustable Shores from Text 4-70

18 Horizontal Bracing of Shores @ 77 Hudson St. Preparing for Fresh Pour on Top Floor

19 Metal Adjustable Shores @ 77 Hudson St. Preparing for Fresh Pour on Top Floor

20 ReShores @ 77 Hudson St. Supporting Floors that have been recently poured and hardened

21 Metal Adjustable Shores @ 77 Hudson St. Supporting Hardened Concrete Floor

22 Metal Adjustable Shores @ 77 Hudson St. Next to open wooden form stairwell

23 Metal Adjustable Shores @ 77 Hudson St. Wood Formed Stairwell

24 Calculations for Shoring and Reshoring Two levels of shoring and one level of reshoring

25 Calculations for Shoring and Reshoring

26 One level of Shoring and Two levels of Reshoring

27 Rules of Calculating Shoring Diagrams Rule#1 – Freshly Poured Concrete transmits it full load to shores below Rule#2 – Hardened Concrete does not deflect until shores are removed Rule#2a – Hardened Concrete does not transmit it loads into columns until shores are removed (taking it own load) Rule#3– Hardened Concrete that deflects and is not connected to ground by shores, shares the load with other floors that are connected. Rule#4– Loads are rebounded (lossed) in Hardened Concrete when connected floors are disconnected by removing shores


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