This is most effective book for students and professionals who pursue study and practices in Structural Engineering. The theory and Problems links with practical approaches and real engineering judgements.
American Society for Civil Engineer (ASCE) has published the latest version (ASCE 7-22) for Minimum Design Load and Associated Criteria for Building and Other Structure describes the means for determining design loads including dead, live, soil, flood, tsunami, snow, rain, atmospheric ice, seismic, and wind loads and their combinations for general structural design. Structural engineers, architects, and building code officials will find the structural load requirements essential to their practice.
Download the Document for Study and Design purpose only.
American Concrete Institute (ACI) has published the Building Code Requirements for Structural Concrete which is the guide for Reinforced concrete structure while designing the structure. It provides the background of material and rationale for the code provision.
ACI has revised the guide after every 3 years. ACI 318-19 is the latest version. Originally it is made in US but many other countries has followed this document. It has two parts, both are incorporated in this document:
Building Code Requirements for Structural Concrete
Commentary on Building Code Requirements on Structural Concrete
Download this Document only for Study purpose and practical help.
d= Effective depth of beam (from centroid of steel in tension zone to topmost fiber of concrete in compression zone).
Note: The value of stress and strain shown in the definition below for each sections of concrete when the section is Design by limit state method (LSM), because it beyond the elast region of stress strain curve.
Definition:“The RCC Section which is reinforced with such amount of steel that when extreme fiber of compression zone of concrete reaches to its permissible allowable stress and strain value (ϵc =0.0035 and fc=0.45fck), the steel provided in tension zone also reaches to its permissible yield allowable strain and stress value (ϵst= (0.002+(0.87fy/Es)) and fs= 0.87fy) at same time then that section will be a Balanced or Critical Section.”
The failure of such section may be due to compression or tension. So balanced section is basically the combination of both brittle and ductile section.
The Neutral Axis of such sections lies in the middle of the section (n=nc) is called Critical Neutral Axis, normally denoted by nc or Xubal.
The Moment of resistance (Mr) of such sections can be determined by Multiplying the lever arm of the stressed section either by Compression force or Tension force because the centroidal of both the areas (Compression and Tension zone) are almost at same distance from neutral axis.
(Moment of Resistance) Mr= Compressive Force*(d-0.42d)
or Mr= Tensile Force*(d-0.42d)
Definition:“The RCC Section which is reinforced with such amount of steel that when extreme fiber of concrete in compression zone reaches to its permissible allowable Strain and stress value(ϵc =0.0035 and fc=0.45fck), while the allowable stresses in steel provided in tension zone doesn’t reaches to its permissible allowable yield strain and stress(ϵst= (0.002+(0.87fy/Es)) and fs= 0.87fy) then that section will be an Over-Reinforced Section.”
It means that the percentage of reinforcement provided more than the requirements.
That RCC element or section will fail due to brittleness which is dangerous to any section.
The section is uneconomical due to high percentage of reinforcement provided.
In such sections the actual Neutral Axis (NA) will move downward below Critical Neutral Axis (Nc) or n>nc.
The Moment of resistance(M r) of such sections will be always more than the Balance section.
(Moment of resistance) Mr=b.n.(fst/2) *(d-n/3)
Definition:“The RCC Section which is reinforced with such amount of steel that when extreme fiber of concrete in compression zone doesn’t reach to its permissible allowable strain and stress value(ϵc =0.0035 and fc=0.45fck), while the allowable stresses in steel provided in tension zone doesn’t reaches to its permissible allowable yield strain and stress(ϵst= (0.002+(0.87fy/Es)) and fs= 0.87fy) then that section will be an Under-Reinforced Section.”
This is the most desirable section(Under-Reinforced) because:
It means that the percentage of reinforcement provided less than the requirements, so saving steel cost.
That RCC element or section will fail in Ductile behavior which is the most desirable condition for any structure.
Show enough warning before failure because first steel has to reach its yield stress before concrete.
The Moment of resistance of such sections will be always less than the Balance section.
In such sections the actual Neutral Axis (NA) will move upward above Critical Neutral Axis (Nc) or n<nc.
Moment of resistance (Mr) of such sections can be determined by considering the stress of steel.
(Moment of Resistance) Mr=fst.Ast(d-n/3)
Note: Now You can evaluate Neutral Axis by the sections given below:
Watch the video… if still any any Query you can comment…Thank You
After reading this blog, you will be able to identify and can execute different types of support in real structure in construction site.
During Engineering you have shown just the idealized form of supports but when you go to construction site you cannot identify and execute different type support in real structures. So in this article your confusion will be vanished. Here we have discussed the most important three (3) types of supports normally used and cause confusion.
(1) Fixed Support
Fixed support mean that it can resist and restrain all the possible movement (vertical, horizontal & bending moment) through the joint/support and the stresses generate in beam due to any type of loading can transfer from beam to column safely. Now we discuss fixed support in Reinforced Cement Concrete Structures (RCC) and Steel Structures:
(a) Fixed Support in RCC Structures
In RCC structure first column concrete is done upto beam bottom level and then after fixing the reinforcements of beam and slab with the column projected rebars then concrete it monolithically so that the member can act as a fixed unit. To identify that the support is fixed or hinged/pin in RCC beam-column joint or the column jointed with foundation, you must check the rebar detail in drawing and on site that if proper development length(Ld) is provided then and the desired ratio of concrete is followed at the site then the support will be consider is fixed. Because the reinforcement at the support will tell you about whether the support is fixed or hinged/pin. The proper development length (Ld) and required concrete grade will achieve sufficient bond/anchorage at that at that joint to resist all the stresses. This type of support is mainly designed to resist bending moment along with the other stresses. You can see the fixed support in the figure below:
(b) Fixed Support in Steel Structures
The phenomena of fixed support that it will resist the possible movements will be same as in the RCC structures. The Steel Beam-Column connections or column-footing connections will be considered as fixed if the bolts or welds around the joint (around the flange and web) are fixed/applied throughout along with gusset plates at that joint/support. If the bolts or welds are fixed/applied only at the web section then it will consider as a hinged/pinned support because it will not resist all the movements (vertical, horizontal or bending moment) except the few one. This type of support is mainly designed to resist bending moment along with the other stresses. Through this type of bolting/welding you provided sufficient anchorage to resist all the stresses. The steel has to resist all the tension not concrete. You can see the Fixed Support in Steel Structure in figure/image below:
(2) Hinge/Pin Support
In this type of support only the horizontal and vertical movements are restrained but cannot resist bending moment. This type of support are not designed for taking any bending moments but just take the axial stresses (axial compression and axial tension). That’s why this type of support is mainly provided only in trusses. But if the bending is not the failure criteria of any member or if the bending moment is not generate sufficiently in any support that it can fail then we provide it in RCC and Steel Frames also:
(a) Hinge/Pin Support in RCC-Bricks Structures
You may have seen that in residential buildings or low storey buildings in which the load bearing component is brick walls then the beams and columns provided there by the unefficient contractor at some areas or in the whole structures is which may be not needed at all and also the structure is not properly designed by the structural engineer. If you look upon the reinforcement at beam-column joints or column-footing joints then you will find that they are not provided any development length or may be not sufficient to developed the required bond/anchorage at the joint. Because the tension is resisted by the steel not concrete. The concrete is also of very low Grade, so that support will not be considered as fixed but it will be a Hinge/Pin Support. But the loads are mainly taking by brick masonry walls that’s why the structure is stable. But you cannot allow this type of supports in RCC frame structures where the load bearing element is beam-column. You can see in given figure:
(b) Hinge/Pin Support Steel Structures
As we have discussed earlier that This type of support are not designed for taking any bending moments but just take the axial stresses (axial compression and axial tension). That’s why this type of support is mainly provided and designed for trusses. But it can be provide in Steel frames Beam-Column and Column-Footing joints when the bending is not the failure criteria. In this type of beam-column joints or column-footing joints the bolts/welds provided only at the web section or flange section of that element which is sufficient to resist the axial stresses. You can see in given figure below:
(2) Roller Support
Roller support can resist only vertical forces. So it is provided only when there is only axially compressive forces are there. You have seen the simply supported beams/girders may be of Steel or RC. The idealized form of simply supported beam is one side is hinge and the other is roller (see image). We consider it because at the hinge/pin side of beam resist horizontal forces because lateral movement are not generate at the element just because of hinge/pin and the other side is roller because due to temperature changes and heavy loads there may be little lateral bit forces occur which causes expansion and bending. If we consider both side is hinged then the temperature stresses in element will cause beam to crack and if we consider both side is roller than little component of lateral force can cause beam/girder to move horizontally which will be unstable. So when the beam which may be RCC or Steel which is lies just on both side support may be brick wall or RCC column but not casted monolithically then that will be an example of simply supported in which one side is roller and the other is hinge/pin support. You can see the roller support both in Steel and RCC structure given below:
Watch the short video given below under these discussion Topics:
Following are some of the important Factors and criteria regarding One-Way Slabs:
Length to Width ratio of the slab should be equal or more than 2 (L/W >= 2)
Load Transfer in One direction (in short direction)
Beams are provided in one direction (along the length)
Main-Bars are provide in short direction because it is the load carrying rebars while the Temperature/Distribution Bars is used in long direction to just cater the unwanted stresses due to temperature or shrinkage.
(2) Two-Way Slabs
Following are some of the important Factors and criteria regarding One-Way Slabs:
Length to Width ratio of the slab should be less than 2 (L/W < 2)
Load Transfer in both direction ( That’s why its called Two-Way Slab)
Beams are provided in both direction.
Main-Bars are provide in both direction because loads are transfer in both direction due to it geometry.
Following are some of the major International Building Codes have been discussed.
(1) General Building Codes
Each cover all aspects of building designing and construction. These codes use by structural designers to make safe and economical their structure while follow the criteria, data required the structural designing and bylaws of the countries they want to design and construct that structure. The following three (3) Codes are the International codes generally follows in different countries in the world for Civil Engineering Structure Designing. Almost every countries has its own building codes which is derived and modified these International Codes according to their countries geography, earthquakes and some other factor and parameters. These Codes specify the requirements of the governmental bodies for minimum design loads on structures and mininmum standards for construction.
(a) Uniform Building Code (UBC-97)
This is an international building code last updated in 1997 that’s why it is called UBC-97. This code is generally applied in USA and Asian Countries. It can be use anywhere in the world if it meets the criteria, data required by the designer and comply with the national and local governments bylaws. So every countries derived and modified these International Codes according to their countries geography, earthquakes and some other factor and parameters. They cannot apply these codes blindly.
(b)International Building Code (IBC-2000)
This code was established in 2000, that’s why it is called IBC-2000. This code is also applicable in different countries throughout the world if it meet the criteria, data required and the local government acceptance. So every countries derived and modified these International Codes according to their countries geography, earthquakes and some other factors and parameters. They cannot apply these codes blindly.
This is an international building code. It is normally applicable in European countries, but it can also be apply in any countries if it meet the criteria, data required and the local government acceptance. So every countries derived and modified these International Codes according to their countries geography, earthquakes and some other factors and parameters. They cannot apply these codes blindly.
Almost every country has its own building codes which is derived and modified these International Codes according to their country geography, earthquakes and some other factors and parameters. They cannot apply these codes blindly. So these derived and modified codes for the specific countries is called National Codes. I want to mention some examples of National Codes.
(a) Building Code of Pakistan (BCP)
BCP code is for Pakistan only and it is derived from UBC-97 because the data and information required for Pakistani Structure Designer was available in UBC-97. Especially the date required regarding earthquakes, so first of all Pakistan publish their Code in 2007 which is called “BCP-SP-07”. So they make little changes in the UBC-97 and publish their own code called BCP.
(B) Indian Standards Code (IS)
IS is the Indian codes for constructions and it is normally applicable in India only unless you make it checked all the criteria to use in any other countries. IS is further divided in many codes normally used for Structural Reinforced Concrete is IS-456-2000, National Building Code (NBC), Bureau of Indian Standards (BIS).
(2) Design Codes or Building Codes for Specific Materials
These codes the cover design and Construction of structures using specific materials. These are the general guideline codes for specific materials. Design codes provides detailed technical standards and are used to established the actual structure design. The ultimate responsibility lies on Structural Engineer that how to apply these standards and his/her efficiency to Design any structure. These Codes include but not limited to:
ACI: American Concrete Institute (Used for RCC structural materials, elements and structures all over the world for design of specific materials guidelines)
AISC: American Institute of Steel Construction ( Manual for Steel Construction structures uses all over the world for general design guidelines)
AASHTO: American Association of State Highway and Transportation Officials (Used for Road designing and Construction all over the world but it should comply with country geography and other parameters).
AREA: American Railway Engineering Association (Manual for Railway Engineering).
AFPA: American Forest and Paper Association ( National Design Association for Wood Construction).
ASTM: American Society for Testing Materials ( general guideline and standards procedures for Testing materials use during Construction)