diff --git a/images/ch2-1.png b/images/ch2-1.png new file mode 100644 index 0000000..ce4306b Binary files /dev/null and b/images/ch2-1.png differ diff --git a/images/ch2-2.png b/images/ch2-2.png new file mode 100644 index 0000000..a0f1fb6 Binary files /dev/null and b/images/ch2-2.png differ diff --git a/images/ch2-3.png b/images/ch2-3.png new file mode 100644 index 0000000..6c6077e Binary files /dev/null and b/images/ch2-3.png differ diff --git a/images/ch2-4.png b/images/ch2-4.png new file mode 100644 index 0000000..35694b8 Binary files /dev/null and b/images/ch2-4.png differ diff --git a/images/ch2-5.png b/images/ch2-5.png new file mode 100644 index 0000000..34ab3d1 Binary files /dev/null and b/images/ch2-5.png differ diff --git a/images/ch2-6.png b/images/ch2-6.png new file mode 100644 index 0000000..faed944 Binary files /dev/null and b/images/ch2-6.png differ diff --git a/input/RectangularBeams.tex b/input/RectangularBeams.tex new file mode 100644 index 0000000..e29bdc2 --- /dev/null +++ b/input/RectangularBeams.tex @@ -0,0 +1,263 @@ +\chapter{Rectangular Beams} +\section{Introduction}Ductile reinforced concrete beams under ultimate loads fail by tension failure modes with +concrete fully or partially crushed. These modes of failure fall in the regions 3, 4 and 4A +(\fig 1.6 and 1.7 of Chapter 1). When moment at a section is small, only tension reinforcement +will suffice. But when compressive force in concrete compression zone is more than the concrete +capacity, compression steel will be required at the compression face of section. Thus reinforced +concrete beams may have two types of sections—singly or doubly reinforced sections. + +\section{Singly Reinforced Rectangular Section} +When the position of neutral axis is such that xu, min S xu S. xu, max \fig \ref{Singly reinforced section 1}, the concrete +compression zone gets subjected to the full concrete stress diagram as given by \fig 21 of the +Code. The equilibrium of the section \fig \ref{Singly reinforced section}. gives, +\begin{equation} +T=Cw +\label{Singly Reinforced} +\end{equation} +\begin{equation} +M_u=C_w.(d-0.42x_u) +\label{Reinforced Section} +\end{equation} +with +\hspace{2cm} $$T=A_st \times 0.87f_y$$ +$$C_w=0.36f_ck\hspace{0.1cm}.\hspace{0.1cm} b\hspace{0.1cm} .\hspace{0.1cm} x_u$$ +and introducing two non-dimensional parameters, +$$\mu=\frac {A_st}{bd} \times 0.87\frac {f_y}{f_ck}$$ +$$k=\frac{M_u}{f_ckbd^2}$$ +\begin{figure} +\centering +\includegraphics[width=0.8\textwidth]{images/ch2-1.png} +\caption{Singly reinforced rectangular section with concrete fully crushed at collapse.} +\label{Singly reinforced section 1} +\end{figure} +%--------------------------------------------------------------------------------------- +\newpage +Equations \eqn \ref{Singly Reinforced} and \eqn \ref{Reinforced Section} give, on simplification, +\begin{equation} +\mu = 0.36n +\label{Concrete} +\end{equation} +\begin{equation} +k=\mu(1-0.42n) +\label{Crushed at collapse} +\end{equation} +These equations are the same as given by the Code in its Appendix G-1.1. The Code has, +however, not made clear that these equations do not apply for low values of n, When the tension +steel strain exceeds the maximum tension steel strain, for the simple reason that the Code +has made no stipulation in this regard. The Code has instead given the provision of the +minimum area of tension reinforcement, +$$\frac{A_s(min)}{bd} = \frac{0.85}{f_y}$$ +which will greatly limit the tension steel strain and thereby restrict cracking and spalling of +concrete of tension zone.\\ +When the position of neutral axis is such that O S xu S xu, min, the concrete compression +zone is subjected to only a part of the standard concrete stress diagram given by the Code and +the above expressions are not valid for this range. The conditions of equilibrium of the section +\fig \ref{Singly reinforced section}give on simplification, +\begin{figure} +\centering +\includegraphics[width=0.8\textwidth]{images/ch2-2.png} +\caption{Singly reinforced rectangular section with concrete not fully crushed at collapse.} +\label{Singly reinforced section} +\end{figure} +\begin{figure} +\centering +\includegraphics[width=0.8\textwidth]{images/ch2-3.png} +\caption{Values for non-dimensional parameters ${\alpha}$,${\beta}$ and ${\gamma}$ \fig \ref{Singly reinforced section}.} +\label{Values for parameters} +\end{figure} +%-------------------------------------------------------------------------------------------- +\newpage +\begin{equation} +\mu=\beta.n +\label{non-dimensional} +\end{equation} +\begin{equation} +k=\mu(1-\gamma.n) +\label{parameters} +\end{equation} +where +\begin{equation} +\hspace{2cm} \beta = \frac{C_w}{f_ck\hspace{0.1cm}.\hspace{0.1cm}b\hspace{0.1cm}.\hspace{0.1cm}x_u} +\label{Beta value} +\end{equation} +\begin{equation} +\gamma = \frac{\bar{x}}{x_u} +\label{stress} +\end{equation} +The concrete stress at the extreme fibre of section \fig \ref{Singly reinforced section} is given by +\begin{equation} +f_c = \alpha.f_ck +\label{extreme fibre section} +\end{equation} +The non-dimensional parameters on $\alpha$, $\beta$, and $\gamma$ can be read from \fig \ref{Values for parameters}, which gives curves for +these parameters with respect to the concrete compression strain at the extreme fibre of section +(81) derived simply by rules of Geometry. + + +Equations \eqn \ref{non-dimensional}and \eqn \ref{parameters} apply when n $<$ $(n_{min})$ and Eqs. \eqn \ref{Concrete} and \eqn \ref{Crushed at collapse} apply when $(n_{min})$ ${\leq}$ n ${\leq}$ $(n_{max})$. +When n $>$ $(n_{max})$, the Code prescribes that n = $(n_{max})$ must be assumed for +ensuring ductility. With n =$(n_{max})$, equation \eqn \ref{Section4} gives the limiting moment of resistance +(M u, am) of singly reinforced rectangular section as, +\begin{equation} +M_{u,lim} = 0.36 n_{max}(1-0.42n_{max})\hspace{0.1cm}.\hspace{0.1cm}f_ck\hspace{0.1cm}.\hspace{0.1cm}bd^2 +\label{Singly R Section} +\end{equation} +\section{Doubly Reinforced Rectangular Section} +When the applied moment $M_u$ is greater than the limiting moment of resistance $(M_{u,lim})$ +of a given singly reinforced rectangular section, compression reinforcement is required to be +provided giving a doubly reinforced section. The equilibrium of the section \fig \ref{reinforced section} gives, +\begin{equation} +T = C_w + C_s +\label{Equillibrium of section} +\end{equation} +\begin{equation} +M_u = C_w(d-0.42x_{u,max}) + C_s(d-d ') +\label{EOSII} +\end{equation} + +\begin{figure} +\centering +\includegraphics[width=0.8\textwidth]{images/ch2-4.png} +\caption{Doubly reinforced rectangular section.} +\label{reinforced section} +\end{figure} +Introducing an additional non-dimensional parameter, +$$\mu' = \frac{A_{sc}}{bd} \times \frac{f_{sc}}{f_{ck}}$$ +These equations give, on simplification, +\begin{equation} +\mu=0.36n_{max} + \mu' +\label{Additional parameter} +\end{equation} +%----------------------------------------------------------------------------------------- +\newpage +\begin{equation} +k=0.36n_{max}(1-0.42n_{max}) + \mu'(1-\frac{d'}{d}) +\label{APII} +\end{equation} +Value of $(f_{sc})$ is to be read from \fig 23 of the Code corresponding to compression steel strain +($\varepsilon_{sc}$), which is given by \fig \ref{Doubly reinforced rectangular section.}, + +\begin{equation} +\varepsilon_{sc} = 0.0035(1-\frac{1}{n_{max}}.\frac{d'}{d}) +\label{Compression steel strain} +\end{equation} +\section{Design Charts} +Equations \eqn \ref{Concrete} to \eqn \ref{parameters} are used to develop charts for singly reinforced rectangular +sections. For an assumed value of n, relevant equations from those given above are used. to +give values for k and $\mu$, which are plotted to give \chartm 2.1 and 2.2, one each for steel types +Fe 250 and Fe 415. For doubly reinforced sections, equations \eqn \ref{Additional parameter} and \eqn \ref{APII} are used to get +values for $\mu$ and k for an assumed value of $\mu’$ and d'/d. These give a series of straight lines for +k, which depend on d'/d, while the straight line for$\mu’$is independent of d'/d . \chartm 2.1 and 2.2 +give all these curves with Y-Y axis representing n or $\mu’$, where n applies for singly reinforced +sections and $\mu’$ for doubly reinforced sections. Values for$(f_{sc})$ are given against values of d'/d in +each chart for ready use. There is an advantage in plotting curves for singly and doubly +reinforced sections on the same co-ordinate axes, in that, the (capacity of a singly reinforced +section need not be specially checked when the applied moment is greater than it. Use of design +charts is illustrated by the following numerical examples. +\section{Numerical Examples} +\begin{example} + Singly Reinforced Rectangular Section (Design) + +\given +b = 30 cm, $(f_{ck})$ = 1.5 $\knpcs$ + + D = 60 cm, $f_y$ = 41.5 $\knpcs$ + +d = 56.25 cm, $M_u$ = 170 $\knm$ + +This example is taken from Design Aids$^{8}$ (Page 11). + +\required$(A_{st})$ + +\solution +$$k= \frac{170 \times 100}{1.5 \times 30 \times (56.25)^2} =0.119$$ +Chart 2.2 gives, +$$n=0.40$$, +$$\mu=0.145$$ +$$A_{st}=\frac{0.145 \times 30 \times 56.25 \times 1.50}{0.87 \times 41.5} = 10.17 cm^2$$ +\end{example} + +\begin{example} Singly Reinforced Rectangular Section (Investigation). + +\given Same as Ex.2.1 with $(A_{st})$= 6.40 cm$^{2}$ + +\required $(M_{u})$ + +\solution +$$\mu=\frac{6.40 \times 0.87 \times 41.5}{30 \times 56.25 \times 1.5} =0.09$$ +Chart 2.2 gives, +$$n=0.245, \mu=0.0775$$ +$$M_{u}=0.0775 \times 1.50 \times 30 \times (56.25^2)/100= 110\knm.$$ +\end{example} +%------------------------------------------------------------------------------ +\newpage +\begin{figure} +\centering +\includegraphics[width=0.95\textwidth]{images/ch2-5.png} +\caption{} +\label{fig:Values for parameters} +\end{figure} +%------------------------------------------------------------------------------- +\newpage +\begin{figure} +\centering +\includegraphics[width=0.95\textwidth]{images/ch2-6.png} +\caption{} +\label{Values for parameters} +\end{figure} +%------------------------------------------------------------------------------------ +\newpage +\begin{example} Doubly Reinforced Rectangular Section (Design). + +\given Same as in Ex. 2.1 but with $(M_{u})$= 320 kNm and d’ = 3.75 cm. This example is taken +from Design Aids$^{8}$(Page 13). + +\required $(A_{st})$, $(A_{sc})$ +\solution +$$k=\frac{320 \times 100}{1.50 \times 30 \times (56.25)^2}=0.225$$ +Chart 2.2 gives for +$$\frac{d'}{d}=\frac{3.75}{56.25}=0.067$$ +$$\mu'=0.0925.\mu=0.265$$ +$$A_{st}=\frac{0.265 \times 30\times 56.25 \times 1.50}{0.87 \times 41.5}=18.58cm^2$$ +For +$$\frac{d'}{d}=0.067$$ +Chart 2.2 gives by interpolation +$$f_{sc}=35.48\knpcs$$ +$$A_{sc}=\frac{0.0925 \times 30 \times 56.25 \times 1.50}{35.48}=6.60cm^2$$ +\end{example} + + +\begin{example} Doubly Reinforced Rectangular Section (Implementation). + +\given Same as in Ex. 2.1 but with $(A_{sc})$=4.0cm$^{2}$ +$$A_{st}=18.0cm^2 \hspace{0.1cm}and\hspace{0.1cm} d'=3.75$$ +\required $M_u$ + +\solution For +$$\frac{d'}{d}=0.067$$ \chartm 2.2 gives, +$$f_{sc}=35.48\knpcs$$ +$$\mu'=\frac{4.0 \times 35.48}{30 \times 56.25 \times 1.50}=0.056$$ +Chart 2.2 gives for $\frac{d'}{d}$=0.067 +$$k=0.19$$ +$$M_u= 0.19 \times 1.50 \times 30 \times (56.25)^2/100=270\knm.$$ +A check on the adequacy of tension steel area is further required. For $\mu'$ = 0.056, \chartm 2.2 +gives +$$\mu=0.23$$ +$$A_{st}(required)=\frac{0.23 \times 30 \times 56.25 \times 1.50}{0.87 \times 41.5}=16.12cm^2$$ +which is less than the provided $(A_{sc})$= 18.0 cm$^{2}$ + +The capacity of the given section is, therefore, correctly computed to be 270 $\knm$. +\end{example} +%----------------------------------------------------------------------------------------- +\newpage +\section{Conclusion} +Design charts have been furnished for singly and doubly reinforced concrete rectangular +beams which are independent of concrete quality and are based on non-dimensional +parameters. These charts are quite concise and incorporate the modifications necessary for +low values of n. Further, these charts can be used with equal ease for design as well as +investigation of a given singly or doubly reinforced rectangular section. + + + + + diff --git a/main.tex b/main.tex index 64774ca..a3854c9 100755 --- a/main.tex +++ b/main.tex @@ -13,5 +13,8 @@ %inputing chapter1 file% \input{input/LimitStateDesign.tex} + + %inputing chapter2 file% + \input{input/RectangularBeams.tex} \printbibliography \end{document} diff --git a/usepackage.tex b/usepackage.tex index bae2c58..ff634cf 100755 --- a/usepackage.tex +++ b/usepackage.tex @@ -25,6 +25,7 @@ \newcommand{\fetwofivezero}{$Fe$ 250} \newcommand{\kn}{kN} \newcommand{\knpms}{kN/m^2} +\newcommand{\knpcs}{kN/cm^2} \newcommand{\knm}{kNm} \newcommand{\mm}{mm} \newcommand{\npmms}{N/mm^2}