What is the maximum height limit for concrete construction for 1 day?

What is the maximum height limit for concrete construction for 1 day?                                

    Sometimes specifiers and inspectors dictate the maximum free-fall distance of concrete because they believe limiting free fall is necessary to minimize concrete segregation. 

    Usually they limit the free-fall distance to 3 to 5 ft (0.9 to 1.5 m), but occasionally the limit is as little as 2 ft (0.6 m). Neither ACI 301- 99, “Specifications for Structural Concrete,” nor ACI 318-02, “Building Code Requirements for Structural Concrete,” limit the maximum distance concrete can free fall. ACI 304R-00, “Guide for Measuring, Mixing, Transporting, and Placing Concrete,” states that “if forms are sufficiently open and clear so that the concrete is not disturbed in a vertical fall into place, direct discharge without the use of hoppers, trunks, or chutes is favorable.” ACI 301, 304, and 318, however, all require placing the concrete at or near its final position to avoid segregation due to flowing. 

At least four field studies have shown that free fall from great distances doesn’t reduce concrete quality.

                                                                    Download IS-CODE 




Comments

Post a Comment

Popular posts from this blog

Design of Structures: Welded Connection

Image
INTRODUCTION The development of welding technology in 1940s has considerably reduced the riveted joint applications. Welding is the method of locally melting the metals (sheets or plates – overlapping or butting) with intensive heating along with a filler metal or without it and allowing cooling them to form a coherent mass, thus creating a joint. A typical weld showing various zones of weld is shown in Fig. 7.1. Such joints can be created to make structures, boilers, pressure vessels, etc. and are more conveniently made in steel. The progress has been made in welding several types of steels, but large structure size may impede the use of automatic techniques and heat treatment which becomes necessary in some cases. Welded ships were made in large size and large number during Second World War and failures of many of them spurted research efforts to make welding a better technology. ADVANTAGES OF WELDED CONNECTIONS The gross sectional area of the welded members is effective since the we
Read more

failure of a rivet joints

Image
Rivet Rivets are short ductile and cylindrical bars that are used for making a permanent mechanical joint. The process of forming a riveted joint is called riveting. A rivet is divided into 3 parts i.e., the head at one end, the tapered tail, and shank, The portion between the head and tail as shown in the figure. As it is a permanent joint it cannot be disassembled without the failure of the machine component. The material of rivet should be tough and ductile. They are usually made of low carbon steel, nickel steel, Brass, Aluminum, copper, etc. Physics Behind Rivetting. The main function of a rivet is to make a connection, That has the strength to prevent failure and tightness to prevent leakage. For connecting “> 2 metal plates, firstly holes are punched and reamed. The plates are then separated to remove any burrs or chips. The cylindrical cold or red-hot rivet is then inserted into the hole. Then the head is backed by a hammer or heavy bar and then the Die as shown in the figur
Read more

What is Rivet Value? and Efficiency of a rivet joint:-

Image
What is Rivet Value? It is defined as the maximum safe force one rivet can withstand. The strength of a rivet in shearing and bearing is calculated and the lesser value is taken as Rivet value. Beyond this value, the rivet will either fail in shear or will be crushed in bearing. the value of shearing and bearing strength one rivet can be calculated from the following relations:- Note :- Rivet value is least of the equations (i) and (ii) Efficiency of a rivet joint:- The original strength of a structural sheet section is reduced by rivet holes provided in it. The efficiency of a rivet joint is the ratio of the strength of riveted joint to the strength of the solid plate(Ex. strength of solid plate without rivet hole). It is denoted by  ɳ  and is expressed as percentage. The effectiveness of a particular riveted joint is measured by the efficiency. Mathematically efficiency is expressed as:                                                                            ɳ  = Strength of joint
Read more