Open Access Open Access  Restricted Access Subscription or Fee Access

A Study on Stress Block Parameters

Manish Kumar Roy


The compressive stress distribution in concrete, when mathematically modeled, can be defined by characteristic parameters known as stress block parameters. There are three such parameters, namely, shape factor, k1, depth factor, k2, and maximum stress factor, k3. There are various shapes of stress blocks, like parabolic, equivalent rectangular, equivalent triangular, and rectangular-parabolic. Various standard codes have adopted an equivalent rectangular stress block, whereas the Indian code has adopted rectangular-parabolic stress block. This paper studies the effect of the shape of stress block on stress block parameters and its impact on flexural and axial capacity of the section based on compressive strength of concrete. The four stress blocks considered for the present study include rectangular-parabolic stress block as per IS: 456–2000, rectangular stress block of ACI 318–14, parabolic stress block of ACI and parabolic stress block proposed by Pul, et al. The compressive strength considered for this study is in the range of 25 to 150 MPa. The results indicate that when a parabolic stress block is transformed into any other shape, the depth factor, and area factor are unchanged because the transformed shape is an equivalent stress block. The flexural capacity is greater as per the parabolic stress block of ACI and minimum for stress block of IS: 456–2000. However, when the axial capacity estimated using stress block of IS: 456–2000 and stress block of ACI 318–14 are compared, it is higher for IS: 456–2000 by about 13%.

Full Text:



Hognestad E, Hanson NW, McHenry D. Concrete stress distribution in ultimate strength design. ACI. 1955; 52: 455–23p.

Oztekin E, Pul, S, Husem M. Determination of rectangular stress block parameters for high performance concrete. Eng Struct. 2003; 25: 371–6p.

Mertol HC, Rizkalla S, Zia P, et al. Characteristics of compressive stress distribution in high strength concrete. ACI Struct J. 200; 105(5): 626–9p.

Khadiranaikar RB, Awati MM. Concrete stress distribution factors for high performance concrete. J Struct Eng. ASCE. 2012; 138: 402–14p.

Yi ST, Kim JJ, Kim JK. Effect of specimen sizes on ACI rectangular stress block for concrete flexural members. ACI Struct J. 2002; 99(05): 701–8p.

Ozbakkaloglu T, Saatcioglu M. Rectangular stress block for high strength concrete. ACI Struct J. 2004; 101(4): 475–9p.

IS: 456–2000. Indian Standard code of practice for plain and reinforced concrete. BIS. 2002.

ACI Committee 318. Building code requirements for structural concrete (ACI 318–14) and commentary (318R-14). ACI. 2014.


  • There are currently no refbacks.