Shear strength of unreinforced concrete

Shear strength of unreinforced concrete

Concrete masonry elements can be designed by using one of several methods in accordance with Building Code Requirements for Masonry Structures ref. This TEK provides a basic overview of design criteria and requirements for concrete masonry assemblies designed using the allowable stress design provisions contained in Chapter 2 of the Building Code Requirements for Masonry Structures.

The content presented is based upon the requirements of the International Building Code ref. Where design assumptions or modeling conditions differ between cited references, they are identified accordingly here. Otherwise, the allowable stress design provisions between the and Building Code Requirements for Masonry Structures are the same.

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This TEK is intended only to provide a general review of the pertinent allowable stress design criteria. Tables, charts, design examples and additional aids specific to the allowable stress design of concrete masonry elements can be found in the TEK listed in the related TEK box, below.

Based on this assumed design model, the internal distribution of stresses and resulting equilibrium is illustrated in Figure 1 for unreinforced masonry and Figure 3 for reinforced masonry.

Utilizing allowable stress design, masonry elements are sized and proportioned such that the anticipated service level loads can be safely and economically resisted using the specified material strengths. The specified strength of masonry and reinforcement are in turn reduced by appropriate safety factors. Minimum design loads for allowable stress design are included in Minimum Design Loads for Buildings and Other Structures ref.

For load combinations that include wind or earthquake loads, the code-prescribed allowable stresses are permitted to be increased by one-third when using the alternative basic load combinations of the IBC. For unreinforced masonry, the masonry assembly units, mortar, and grout if used is designed to carry all applied stresses see Figure 1.

The additional capacity from the inclusion of reinforcing steel, such as reinforcement added for the control of shrinkage cracking or prescriptively required by the code, is neglected. Because the masonry is intended to resist both tension and compression stresses resulting from applied loads, the masonry must be designed to remain uncracked. Allowable flexural tension values as prescribed in Building Code Requirements for Masonry Structures, vary with the direction of span, mortar type, bond pattern, and percentage of grouting as shown in Table 1.

For assemblies spanning horizontally between supports, the code conservatively assumes that masonry constructed in stack bond cannot reliably transfer flexural tension stresses across the head joints. As such, the allowable flexural tension values parallel to the bed joints perpendicular to the head joints for stack bond construction are assumed to be zero for design purposes unless a continuous section of grout crosses the head joint, such as would occur with the use of open-ended units or bond beam units with recessed webs.

Because the compressive strength of masonry is much larger than its corresponding tensile strength, the capacity of unreinforced masonry subjected to net flexural stresses is almost always controlled by the flexural tension values of Table 1.

For masonry elements subjected to a bending moment, Mand a compressive axial force, Pthe resulting flexural bending stress is determined using Equation 1. If the value of the bending stress, f bgiven by Equation 1 is positive, the masonry section is controlled by tension and the limiting values of Table 1 must be satisfied.

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While unreinforced masonry can resist flexural tension stresses due to applied loads, unreinforced masonry may not be subjected to net axial tension, such as that due to wind uplift on a roof connected to a masonry wall or the overturning effects of lateral loads.

While compressive stresses from dead loads can be used to offset tensile stresses, reinforcement must be incorporated to resist the resulting tensile forces when the element is subject to a net axial tension. When masonry elements are subjected to compressive axial loads only, the calculated compressive stress due to applied load, f amust not exceed the allowable compressive stress, F aas given by Equations 3 or 4, as appropriate.

A further check for stability against an eccentrically applied axial load is included with Equation 5, whereby the axial compressive load, Pis limited to one-fourth the buckling load, P e.

shear strength of unreinforced concrete

With Equation 5, the actual eccentricity of the applied load, eis used to determine P e.Eurocode Applied. The characteristic compressive strength f ck is the first value in the concrete class designation, e. The strength classes of EN are based on the characteristic strength classes determined at 28 days.

The characteristic compressive cube strength f ck,cube is the second value in the concrete class designation, e. The mean compressive strength f cm is related to the characteristic compressive strength f ck as follows:. The tensile strength under concentric axial loading is specified in EN Table 3.

The variability of the concrete tensile strength is given by the following formulas:. The elastic deformation properties of reinforced concrete depend on its composition and especially on the aggregates. The values of E cm given in EN should be regarded as indicative for general applications, and they should be specifically assessed if the structure is likely to be sensitive to deviations from these general values.

The minimum reinforcement is required to avoid brittle failure. Sections containing less reinforcement should be considered as unreinforced. Please select a previously saved calculation file. Make sure that the selected file is appropriate for this calculation.

STRENGTH DESIGN PROVISIONS FOR CONCRETE MASONRY

Ok Cancel. You can provide the following project data as page header. Use current date. Print Close. Steel characteristic yield strength. Affects minimum reinforcement ratios. Concrete partial material safety factor. It affects concrete design strengths. Note: Always verify the validity of the Nationally Defined Parameters. Please inform us of any discrepancy using our Contact Form. Calculate Finished Recalculate Loading This minimum reinforcement is required in order to avoid brittle failure.

It is applicable for beams even if design shear reinforcement is not required. For slabs it is applicable only for slabs where design shear reinforcement is required.

It corresponds to the notional area b w s where b w is the width of the web and s is the spacing of the shear reinforcement along the length of the member. Characteristic compressive strength f ck The characteristic compressive strength f ck is the first value in the concrete class designation, e.

shear strength of unreinforced concrete

Characteristic compressive cube strength f ck,cube The characteristic compressive cube strength f ck,cube is the second value in the concrete class designation, e. Characteristic tensile strength The tensile strength under concentric axial loading is specified in EN Table 3.Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro.

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shear strength of unreinforced concrete

Privacy We don't collect information from our users. Citation This page can be cited as Engineering ToolBox, Concrete - Properties. Modify access date. Scientific Online Calculator.Log In. Thank you for helping keep Eng-Tips Forums free from inappropriate posts. The Eng-Tips staff will check this out and take appropriate action. Click Here to join Eng-Tips and talk with other members! Already a Member?

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Students Click Here. Related Projects. Hello I am struggling to find the shear capacity of a concrete section with no shear or tensile reinforcement at all and was wondering if anyone can help me with it.

Could anyone please help? It can be any type of shear, either punching or usual shear from beam loading? One small shrinkage crack could change your answer completely.

Can you not get a couple of bars in somewhere??Concrete masonry elements can be designed using one of several methods in accordance with Building Code Requirements for Masonry Structures ref. This TEK provides a basic overview of design criteria and requirements for concrete masonry structures designed using the strength design provisions contained in Chapter 3 of the edition of Building Code Requirements for Masonry Structures also referred to as the MSJC Code ref.

In addition, changes to the strength design method incorporated into the edition of the MSJC Code ref. Strength design is based on the following design assumptions in conjunction with basic principles of engineering mechanics refs. Based on the prescribed design model outlined above, the internal distribution of stresses and strains is illustrated in Figure 1 for a reinforced masonry element. A more comprehensive review of the design model is provided in Masonry Structures, Behavior and Design ref.

Using strength design, the design strength of a masonry element is compared to the required or factored strength indicated by the subscript uwhich includes load factors to account for the uncertainty in predicting design loads and the probability of more than one design load acting simultaneously. The required strength is based on the strength design load combinations as required by Section of the IBC. For strength design, these load combinations are effectively the same.

The design is acceptable when the design strength equals or exceeds the factored strength i.

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The following sections cover the general strength design requirements applicable to both unreinforced and reinforced masonry assemblies, with the exception of design requirements for anchor bolts and lap splices. Strength reduction factors are used in conjunction with the load factors applied to the design loads.

The values of the strength reduction factors for various types of loading conditions are:. When designing for earthquakes, the story drift the relative displacement of adjacent stories must be checked against the IBC prescribed allowable story drifts. For masonry buildings with cantilevered shear walls, the IBC limits the story drift to 0.

For other types of masonry shear wall buildings, except masonry frames, the allowable story drift is limited to 0. Second order effects due to P -delta contributions must also be taken into account, which is usually accomplished through iteration until convergence is achieved. As such, any rational method of determining cracked section properties is permitted. For use in Equations 1 and 2, the cracking moment can be taken as:.

Where the modulus of rupture, f ris obtained from Table 1 for the type of mortar and construction under consideration. The actual yield strength of the reinforcement is limited to 1.

RCD:- Design of a Square reinforced concrete column based on ACI codes part 1/2

The combination of these requirements effectively precludes the use of bed joint reinforcement to be used as primary structural steel in masonry designed by the strength design method, because the nominal yield strength of bed joint reinforcement exceeds these limits. The compressive resistance of steel reinforcement is not permitted to be used unless lateral reinforcement is provided in compliance with Chapter 2 of the MSJC Code, except as permitted when checking the maximum reinforcement limits as described later.

For unreinforced masonry, the masonry assembly units, mortar and grout, if used is designed to carry all applied stresses. The additional capacity from the inclusion of reinforcing steel, if present such as reinforcement added to control shrinkage cracking or prescriptively required by the codeis neglected when designing unreinforced masonry elements.

Because the masonry resists both tension and compression stresses resulting from applied loads, the masonry must be designed to remain uncracked. These values apply to masonry subject to out-of-plane bending. For this case, the modulus of rupture of the grout is taken equal to psi kPa. Likewise, for masonry subjected to in-plane bending, the modulus of rupture normal and parallel to the bed joints is taken as psi kPa.

Conversely, if F u as given by Equation 4 is negative, the masonry section is in compression and the design compressive stress of 0. When unreinforced masonry walls are subjected to compressive axial loads only, the nominal axial compressive strength, P nis determined using equation 5 or 6, as appropriate. Unreinforced masonry is not permitted to carry net axial tension forces.Log In.

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shear strength of unreinforced concrete

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Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. Can anyone tell me the procedures, assumptons, and formulas to use when checking a thick unreiforced concrete slab.

I am thinking that if the slab is thick enough you just need to check the shear values because the tension steel will not develope. Is there a ratio of length to depth, or other guidlines on when this assumtion is correct?

Any help would be greatly appreciated. ACI has a section on the design of plain unreinforced concrete.Log In. Thank you for helping keep Eng-Tips Forums free from inappropriate posts. The Eng-Tips staff will check this out and take appropriate action.

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ALLOWABLE STRESS DESIGN OF CONCRETE MASONRY

Join Us! By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. Home Forums Structural Engineers Activities Structural engineering general discussion Forum punching capacity of unreinforced slab thread Unless it is too early and I am not thinking clearly, isn't this just the punching shear capacity of the concrete?

This will be laid out in any concrete design textbook. As is included in this relationship. Are you dealing with RC concrete or just plain?

In doing a new spread footing design I usually select the depth of the footing based on punching or wide beam shear. When doing the initial design, I only use the plain concrete to calculate the shear capacity. Agree with ToadJones. Typical method in North American codes of dealing with punching shear is to consider the concrete only unless shear reinforcement studs, vertical ties, etc.

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