Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 SCHOOL OF ENGINEERING & BUILT ENVIRONMENT SESSION 2020-2021 MEng/BEng(Hons) Computer Aided Mechanical Engineering MEng/BEng(Hons) Mechanical-Electronic Systems MEng/BEng(Hons) in Mechanical & Power Plant Systems BEng(Hons) in Design & Manufacture (GA) ENGINEERING DESIGN & ANALYSIS 4 MATRIX ANALYSIS OF STRUCTURES Dr David R Gordon Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 1 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 MATRIX ANALYSIS OF STRUCTURES A Structure is an assembly of individual elements or beams connected together and supported by different types of support such as fixed ends, roller support, pinned support etc. Matrix Analysis as described here requires an understanding of the possible deformation (internal) mechanisms (degree of freedom’s or dof’s) of a particular structure. Based on a knowledge of how each ‘dof’ causes each individual element or beam of the structure to bend or flex etc. allows the derivation of the overall stiffness matrix [K] for the whole structure. The analysis involves understanding the impact these deformations have on the structure. The next step is to derive the loading vector [P] for the structure based on the type of loading acting on each beam element (internal ‘reactive’ or externally applied ‘active’) and the impact of end restraints or support conditions have on the magnitudes and formulae used. The equilibrium equation in Matrix form is therefore: [ P ] [ K ][ ] The structure is then solved by obtaining the actual values of the identified dof’s [∆] from: [] [ K ]1[ P] and using this information to then determine the forces, moments etc. acting on each individual element or beam which together forms the entire structure. Effectively having solved for the unknown displacements the structure has been solved and can be now broken up into each individual beam or element. The process follows closely that used in Finite Element Analysis (FEA) applications but with the hand calculations the number of dof’s is massively reduced to produce a 2x2 or 3x3 matrix which can be more easily manipulated mathematically. The lecture series follows the process as described above and will concentrate on firstly the Stiffness matrix [K] derivation using the equations as derived from the slope deflection equations and obtained from the generated DATASHEET. The next step is the determination of the loading vector [P]. Finally the problem can be solved from a determination of the dof’s [∆] and then can take several different routes to obtaining all/some reactions and action diagrams such as Thrust, Shear Force and Bending Moment Diagrams as required. Understanding the nature of Free and reactive effects are important in assembly of the above diagrams. The analysis is explained through a number of worked examples. Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 2 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 In the 19th century the accent was upon the development and application of structural theory based on the mathematical background laid earlier. Important contributions were made by Navier, Clapeyron, Saint-Venant, Airy, Maxwell, Castigliano, and Mohr amongst others. Their work continues to form the basis of structural theory. Unfortunately, analytical solutions using the fundamental theories can only be obtained to a limited class of structures of simple geometry, and direct numerical solutions require computing power which was not available until comparatively recently. Consequently in the first half of this century engineers turned their attention to developing a variety of indirect methods of solution to particular classes of problem, e.g. the skeletal structure (assembly of bar/beam components). The slope deflection equation (G A Maney) appeared but were limited to very simple problems due to impossibility of solving large sets of linear algebraically simultaneous equations. This was of course until the advent of the use of the digital computer. Also because of their limitation the Moment Distribution Method was derived (Hardy Cross) which avoided the solution of a large set of equations. From the period around 1950 the development of the digital computer presented the structural analysis with ever increasingly powerful aid in solving problems. This led to methods of analysis tailored to the computer, which were direct and general in application. Matrix algebra provided a basis for the efficient organisation and manipulation of large quantities of data. The stage was set for the introduction of matrix methods of structural analysis. In general these relate to the analysis of skeletal structures. The matrix methods require the generation of relationships (in matrix form) linking forces (reactions, moments etc.) at the ends of generic element members in a skeletal structure to the corresponding displacements. Relationships can be found for a straight member of uniform cross section that are ‘exact’: that is the relationships represent an exact solution at all points of the differential equations governing the deformation of such a member. Then the relationships for each member of the structure can be combined following certain rules (of equilibrium and compatibility) into a system of simultaneous equations for the whole structure, and the solution of these effectively gives the exact solution for the theoretical model structure. Two kind’s of approach are commonly used. In the matrix displacement (or stiffness or equilibrium) method the member relationships are those for end forces expressed in terms of end displacements by way of a stiffness matrix and the unknown quantities in the set of equations for the whole structure are displacements at nodes or joints. In the matrix force (or flexibility or compatibility) method the member relationships are those for end displacements expressed in terms of end forces by way of a flexibility matrix and the unknowns are forces. The matrix displacement method is the more popular method and adopted here. Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 3 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 SLOPE DEFLECTION EQUATIONS FOR FLEXURAL DEFORMATION Consider the generalist beam which forms the generalised deflected shape indicated and the associated reaction forces and moments with all deformations and force/moment directions’ +ve convention as indicated. (M1+M2)/L L x M1 δ Θ2 Θ1 x M2 x -(M1+M2)/L Consider the section x-x at distance ‘x’ from the LHS. M M2 M xx M 1 1 .x L d2y M M2 EI 2 M xx M 1 1 .x L dx EI dy M M2 2 M 1 .x 1 .x A dx 2 . L x 2 M1 M 2 3 EI . y M 1 . .x A.x B 2 6.L Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 4 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Boundary Conditions: X = 0, y1 = y = 0 X = 0, dy = dx Θ1 0 0 0 0 B B 0 EI1 0 0 A EI1 A M M2 L EI2 M1L 1 EI1 L 2 (1) L2 M 1 M 2 L3 EI . M 1 EI1.L 2 L 6 (2) 2 dy X = L, = dx X = L, y = Θ2 δ Solving equations (1) and (2) for M1 and M2 gives the generic SLOPE DEFLECTION EQUATIONS: 2 EI 3. 2.1 2 L L 2 EI 3. M2 2. 2 1 L L M1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 5 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Note: this is the derivation for information! from (1) M M2 L EI 2 M 1 L 1 EI1 0 L 2 L L M 1 M 2 EI1 EI 2 0 2 2 2 EI1 2 EI 2 M1 M 2 (3) L L 2 from (2) and substitute (3): 2 EI1 2 EI 2 (M 2 ) M2 3 2 EI1 2 EI 2 L2 L L L EI1.L EI . ( M 2 ) L L 2 L 6 2 2 2 L L EI1 L EI 2 L L EI . M 2 EI1.L EI 2 L M 2 M 2 EI1.L 2 6 3 3 6 2 2 2 L L L L L EI . M 2 EI1 L L EI 2 ( L ) 3 3 2 6 6 L 2L 3 11 EI . M 2 EI1 EI 2 6 3 3 L2 L 2L EI1 EI 2 6 3 3 L 2L 6 M 2 EI1 EI 2 EI . 2 3 3 L 2 4 6 EI . M 2 EI1 EI 2 2 L L L 2 EI 3EI . M2 2 2 1 (4) L L EI . M 2 from (3) and substitute (4): 2 EI1 2 EI 2 L L 2 EI1 4 EI 2 6 EI . 2 EI1 2 EI 2 M1 L L L L L2 4 EI1 2 EI 2 6 EI . M1 L L L2 2 EI 3EI . M1 21 2 (5) L L M1 M 2 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 6 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 It is very important to establish a sign convention for all Moments, Forces and Member Rotations etc. in any structural configuration when problem solving and avoid confusion: + ve + ve All Moments (M1, M2,) Rotations (Θ1 Θ2) and member rotation (δ/L) are designated CLOCKWISE POSITIVE. Also reaction forces are positive downwards! They follow the generic beam described earlier There are some important ‘Special Cases’ which can help to solve structural Problems to situations which arise frequently in Structures (and these helpful equations are included in the associated DATASHEETS for our specific use): Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 7 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Member subject to a rotation at ONE END ONLY (Θ1) with no member Rotation (δ/L = 0). a) δ=0 (M1+M2)/L L Θ2=0 M1 M2 Θ1 (M1+M2)/L M1 2 EI 3. 4 EI .1 2.1 2 L L L M2 2 EI 3. 2 EI . 1 2. 2 1 L L L M2 M1 2 Hence, a carry over equal to one half of the applied moment to the other end when a pin joint is introduced to an initial fixed end. This is useful for whenever a fixed end is ‘released’ to become a pin connection. (See later examples) e.g: +M +M/2 +M +M -M -M ** = pin δ=0 6 EI L2 L Δ2=0 M1= 4 EI L M2= Δ1=1 4 EI L 6 EI L2 4 EI L 2 EI L 2LEI 6 EI 2 L L 6 EI L2 2 EI L See Datasheet, item 2, p12 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 8 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 b) Member subject to no end rotation at EITHER END (Θ1=0 etc) but experiences whole member Rotation only occurring (δ/L). (M1+M2)/L Θ2=0 L M1 δ M2 Θ1=0 (M1+M2)/L M1 2 EI 3. 6 EI . 2. 1 2 L L L2 M2 2 EI 3. 6 EI . 2. 2 1 L L L2 12 EI L3 M1= 6 EI2 δ=1 L Δ1=0 M2= 6 EI2 L 12 EI L3 Δ2=0 12 EI L3 12 EI L3 M1= 6 EI2 L M2= 6 EI2 L See Datasheet, item 3, p12 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 9 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 c) Member with one end pinned and member subject to both Θ1 and member Rotation occurring (δ/L). (M1)/L L M1 δ Θ1 Pin M2=0 (M1)/L 2 EI 3. 2. 1 2 L L 2 EI 3. M2 2. 2 1 0 L L 1 3. M1 2 Hence: 2 2 .L M1 2 EI L 1 3. 3. 2.1 2 2 . L L M1 3EI 1 L L (Observe the attached DATASHEET on page 12, items 5 and 6 for consistency) This DATASHEET provides the information to enable the speedy determination of the Overall Stiffness Matrix for a given structure. Note: For the case when a beam has a pinned end the rotation at the pin equals –ve ½ of the rotation at the other end: 2 Θ1 1 2 : 2 1 2 ** pin Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 10 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 DETERMINATION OF THE STIFFNESS MATRIX ‘K’ and PROBLEM SOLVING The assembly is derived on a basis of compatibility and equilibrium. This condition simply states that the displacement of any point of a loaded structure must be compatible with the overall displacement of the whole structure. The displacement must therefore be continuous and single valued everywhere such that the structure still ‘fits together’ under load. The following is thus required: Within each region the displacement varies smoothly with no discontinuities. At the boundaries between neighbouring regions the displacements match each other in a manner consistent with the problem. At the structure boundaries the prescribed displacements are satisfied. Process: 1. 2. 3. 4. 5. 6. 7. 8. [K].[Δ] = [P] Determine the Non-Zero displacements in the P, Δ system. The solution strategy is to firstly determine the stiffness matrix [K] for the whole structure in terms of the unknown dof Apply each Δ = 1 in turn (all other Δ set to zero) to produce the appropriate rows/columns of the[K] matrix. Then determine the load vector [P] for the whole structure in terms of these unknown displacements. Having determined the [K] and [P] matrices the solution of the structural problem can be completed by solving the following matrix [] [ K ]1. [ P] equation for the loading P: Evaluate the displacements [Δ] from the transposed matrix equation. Use the slope deflection equations to determine the actual moments existing at the nodes (at the various Δ locations). Use these moments and known forces to establish the final reaction forces from basic equilibrium equations. All problems are tackled in the same manner irrespective of the actual configuration. The support and loading conditions are adapted as necessary. The method above will be illustrated through the following two worked examples. The first is for a simple 1 dof problem and the second to establish the stiffness matrix [K] for a 3 dof problem. Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 11 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Simple ONE DoF Example: ALL MEMBERS HAVE THE SAME CROSS SECTIONAL, AND MATERIAL, PROPERTIES, EI = 104 kNm2 The structure is the simplest that we could analyse as it only has one degree of freedom. Due to the supports at A, C, D and E the structure cannot translate upwards, downwards, left or right. There is only ONE connected joint at B and therefore only the rotation of this joint is the unknown displacement for the structure. Also, due to the fixed end connections at A, D and E there is no rotations ( A , D , E 0 ). The rotation at C is initially unknown, however this will be obtained after the rotation 1 2 at B is determined, since C B 2m 3m 6m D 3m 40kN A 4m B C pin-jointed connection 30kN/m E Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 12 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Solution: 1- Determine the stiffness matrix [K]. Identify the one DoF as the rotation at B: e.g: 2m 3m 6m D 3m A 4m B 1 40kN C pin-jointed connection 30kN/m E Remove all loading and apply a +ve CW rotation ONLY to the structure AT THE DELTA-1 POSITION, and accurately observe the distorted, deflected shape each beam member takes up. (DEMONSTRATED IN CLASS) D A B C E Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 13 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Reference the DATASHEET 1 of 2 for the correct coefficients with (unity). e.g: =1 Beam members AB and BD (rotate the DATASHEET image 90 degrees clockwise to match): Member BC: Member BE (rotate the DATASHEET image 90 degrees clockwise to match): Stiffness coefficients for Delta-1, kAB + kBD + kBC + kBE = 4 EI AB 4 EI BD 3EI BC 4 EI BE 4 EI 4 EI 3EI 4 EI 4.67 EI = 2 3 9 4 L AB LBD LBC LBE [K]=4.67 EI Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 14 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 2 - Next we need to determine the corresponding LOADING VECTOR [P]: ‘Explode’ the structure into individual beam elements: BOOM! We are now looking for the ‘MOMENTS’ from DATASHEET 2 of 2 and which correspond with the rotational position of Delta 1, i.e [P1] at B. (NOTE: ‘FORCES’ correspond to translational displacements if appropriate) D 3m 3m 2m 6m 40kN 0 A wL2 12 30 4 2 12 40 kNm 4m C B 0 Wab 2 1 Wa 2 b 2 2 L2 L 40 3 6 2 1 40 3 2 6 2 92 92 53.33 13.33 66.663 kNm 30kN/m E Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 15 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 [P1]=[ EXTERNAL (as applied) - INTERNAL (as reactive) ] [P1]=[ 0 - (+40 – 66.663) ] [P1]= [ 0 - (-26.663) ] [P1]= [ +26.663 ] 3 – Determine the value for the rotation at B: 1 K 1 P1 1 5.709 26.663 5.709 10 4 rads 4.67 EI EI 4 – We can determine the bending moment for ANY point in the structure: e.g: MBC 2m 3m 6m D 3m 40kN A 4m B C MCB=0 pin-jointed connection 30kN/m E M BC 2 EI L 3 F 2 B C L M BC 2 104 1 2 5.709 10 4 5.709 10 4 0 (66.663) 9 2 M BC 1.903 66.663 64.76 kNm Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 16 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 TYPICAL DATASHEET page 1 of 2 -6EI/L2 6EI/L2 2EI/L 4EI/L 6EI/L2 -6EI/L2 4EI/L 2EI/L -12EI/L3 12EI/L3 -6EI/L2 12EI/L3 -12EI/L3 6EI/L2 6EI/L2 3EI L3 -3EI L2 3EI L3 3EI L2 3EI L -6EI/L2 3EI L2 3 2 1 2 2L M 3EI L L Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 17 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 EXAMPLE 1 Develop the total stiffness matrix for the structure shown: L I I L/2 2I L Pinned end Fixed end The Structure has THREE potential INTERNAL degrees of Freedom (dof), Δ1, Δ2, Δ3 as shown from within the assembled structure and EXCLUDING any at the supports. The stiffness matrix components (rows and columns) are derived by applying only one ‘dof’ to the structure with all others set to zero. The resulting deformation state should for each element conform to one of the standard beam derivations listed in the Datasheet. Δ2 Δ1 L Δ3 I L/2 I 2I L Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 18 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 e.g: For the first column apply Δ1 (δ) = 1 (unity), and the other Δ’s =0 Δ1=1 I L/2 I L 2I 3EI L3 -3EI L2 Element 1 matches the fifth image in the DATASHEET, e.g: 3EI L3 Element 2 (Horizontal beam) is not distorted by this imposed deformation 12EI/L3 12EI/L 3 Element 3 matches the third -6EI/L2 image in the DATASHEET, e.g: Hence, the matrix components are given by: k11 3EI 12 E (2 I ) 24 EI 24 EI 48 EI 3 3 3 ( L2 ) 3 L3 L L L i.e. in the same +ve direction as Δ1 . Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 19 -6EI/L2 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 similarly: k 21 3EI 12 EI 12 EI . or . ( L2 ) 2 L2 L2 k31 6 E (2 I ) 12EI L2 L2 48 EI L3 12 EI giving column 1 as: 2 L 12 EI L2 ? ? ? ? ? ? For Column 2, apply Δ2 (θ) = 1 (unity), and the other Δ’s =0 Δ2=1 I I 2I 3EI ( L2 ) 2 3EI ( L2 ) 3EI L2 3EI L 4 EI L 2 EI L 6EI/L2 4EI/L k12 -6EI/L2 2EI/L 3EI 3EI 12 EI ( L2 ) 2 ( L2 ) 2 L2 (in the direction of +ve Δ1) Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 20 3EI L2 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 k 22 3EI 4 EI 6 EI 4 EI 10 EI ( L2 ) L L L L k 32 2 EI L (in the direction of +ve Δ2) (in the direction of +ve Δ3) Giving [K], by adding column 2, as: 12 EI L2 10 EI L 2 EI L 48 EI L3 12 EI 2 L 12 EI L2 ? ? ? For Column 3, apply Δ3 (θ) = 1 (unity), and the other Δ’s =0 Δ3=1 I I 2I 2 EI L 4 EI L 6 EI L2 4 E (2 I ) L k13 6 E (2 I ) 12 EI 2 2 L L k 23 2 EI L k 33 4 EI 4 E (2 I ) 12 EI L L L This give the final column 3 and completes the matrix. 48 EI L3 12 EI 2 L 12 EI L2 12 EI L2 10 EI L 2 EI L 12 EI L2 2 EI L 12 EI L = 48 L3 12 EI 2 L 12 L2 12 L2 10 L 2 L Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 12 L2 2 L 12 L Page 21 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 TUTORIAL 1 – MATRIX ANALYSIS OF STRUCTURES Develop the total stiffness matrix for the structures below: 1. All span lengths = L A B 24 3 L 6 2 L 6 2 L I 3I C 2. I L 6 L 16 L 6 2 L 16 6 L L 2 D EI = Constant for all members D L/2 A 6 L/2 B L C 108 L3 24 2 L 6 2 L 24 L 12 2 L 2 L 14 L 6 2 L L 2 L E 3. E 2I 8L 12L D C 3I 6L 2I 2I 59 3 288 L 1 2 3L 0 1 7 1 3L2 3L 2L 8L B A Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 22 0 1 2L 3 L Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 External Loading Considerations As has been indicated above the total stiffness matrix for a structure can be obtained by inspection. This technique made direct application of the slope deflection equations. As derived the equations did not reflect the effect of loading applied externally to the structure since it was reactive to imposed possible displacements. The presence of external loading causes additional end moments, called Fixed End Moments. These are normally and easily calculated from standard beam formulae as indicated and provided in DATASHEET-page 2 of 2. The fixed end moments are to represent the reactive response of members due to loads and can be written in Matrix form [P] to align with the derived stiffness matrix. Thus in their reactive role the slope deflection equations are modified as follows: 2 EI 3. F 2.1 2 M1 L L 2 EI 3. F M2 2. 2 1 M2 L L M1 Careful attention should be paid to the signs of MF when using MF in this context as the sign is embedded in the modified slope deflection equations above. (see examples) The loading matrix is the direct representation of the loads acting at, and in the direction of, the identified degrees of freedom (Δ1, Δ2, Δ3, etc.) and equation then becomes: P1 P [ P] 2 . Pn F1 F2 . Fn EXT INT where Pn are the applied external or ‘active’ moments/loads (concentrated) and F the internal or ‘reactive’ moments/loads. Action and re-action are equal but opposite and hence the –ve sign We are now ready to complete the full analysis for a structure [ P ] [ K ][ ] , or [] [ K ]1[ P] as outlined in the following example 2: Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 23 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 DATASHEET page 2 of 2 (contd.) (FIXED END MOMENTS) w wL2/12 -wL2/12 wL/2 wL/2 W WL/8 -WL/8 W/2 W/2 W Wa2b/L2 -Wab2/L2 Wb/(a+b) Wa/(a+b) B A F M AB 21 M FBA M AB 2EI 3 F 2 1 2 M AB L L Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 24 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 EX.2. The Frame shown below is rigidly fixed at D and E and is supported by a tie bar at C. All members have the same flexural rigidity (EI) of 10 MNm2. Considering flexural deformation only (i.e bending action), and using the Displacement (Stiffness) method of Matrix Analysis determine: i) the rotations at B and C ii) the magnitude and nature of the force in the tie bar FC. F 10kN 5kN/m D B A C 10m E 10m 5m 10m The structure has two unknown displacements (2 DoF). i.e rotations at B and C. Δ1 i) Apply Δ1=1 with Δ2 =0 2EI 4EI 10 10 Δ2 Δ1=1 4EI 10 Δ2=0 k11 4(10) 4(10) 8 10 10 k 21 2(10) 2 10 2EI 10 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 25 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 ii) Apply Δ1=0 with Δ2 =1 2EI 10 4EI 10 Δ2=1 Δ1=0 4EI 10 2EI 10 Hence: k12 2(10) 2 10 k 22 4(10) 4(10) 8 10 10 8 2 [K ] 2 8 And, [P] = [K] [Δ] [ K ] 1 1 DET [Δ] = [K]-1 [P] or 8 2 1 2 8 2 (8 8) (2) 8 2 1 8 2 2 8 60 2 8 1 1 8 2 P1 60 2 8 P 2 2 Examine the external loading on the structure and determine the [P] matrix. F 10kN 5kN/m D B A C wL2 5 10 2 12 12 41.7.kNm 10 x 5 = 50kNm E 5m 10m 10m (41.7) 50 41.7 91.7 91.7 10 3 P1 50 . kNm .MNm P 0 (41.7 41.7) 0 0 0 0 2 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 26 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 1 1 8 2 91.7 10 3 0 2 60 2 8 8 91.7 10 3 0.01223.rads 60 2 91.7 10 3 2 3.0567 10 3.rads 60 1 Slope deflection equations: -41.67 +41.67 2 EI B [2. B C ] M F BC L 2 10 [2 0.01223 (3.057 10 3 )] (41.67 10 3 ) 10 1.136 10 3 MNm 1.136.kNm M BC M BC M BC C 2 EI [2. C B ] M F CB L 2 10 [2 (3.057 10 3 ) (0.01223)] (41.67 10 3 ) 10 53.9 10 3 MNm 53.9.kNm M CB M CB M CB 2 10 [2 (3.057 10 3 ) (0)] (41.67 10 3 ) 10 53.9 10 3 MNm 53.9.kNm M CD M CD 2 10 [2 0 (3.057 10 3 )] (41.67 10 3 ) 10 0.03556.MNm 35.56.kNm M DC M DC B Free Body Diagrams: 5kN/m wL/2 = 25kN 10m 5kN/m C 25kN 25kN + 1.136 (1.136+53.9)/10 = 5.5036 kN 53.9 = 19.4964 kN 30.504 kN 35.56 1.834 kN Hanger Force = 57.34 kN Tension 25kN + 53.9 5.5036 kN 10m D 26.834 kN Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 1.834 kN 23.17 kN Page 27 BENDING MOMENT DIAGRAMS FOR BCD Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 FREE BMD Free bending moment for parabola: wL2 5 10 2 M max 62.5kNm 8 8 5kN/m B C 5kN/m 10m D 10m 62.5 62.5 REACTIVE BMD + + 1.136 53.9 53.9 35.56 COMBINED OR, FINAL BMD FOR BCD +62.5 62.5 26.382 36.118 +36.118 62.5 44.73 17.77kNm +17.77 +1.136 -35.56 53.9 1.136 26.382kNm 2 -53.9 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 35.56 53.9 35.56 44.73 2 Page 28 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 EX 3. The structure ABCDE shown in Figure I has roller supports at A and C which also provide for a pinned connection at A and C, is fully fixed at E, and carries a uniformly distributed load of 5kN/m along member BC. A discrete offset force of 32 kN is applied at D, and a force of 12 kN is applied to the rigid cantilever bar BF at F. The members have their relative flexural rigidities as shown, where EI is 10MNm2. Determine: (a) the stiffness matrix [K] for the structure using the Displacement (Stiffness) method of matrix analysis and considering flexural deformation only; (b) the load vector [P] for the applied loading; (c) the reactions at supports A, C and BMD for AB and BC. Note: Use may be made of DATASHEET Q.1 EI 2EI 3EI Figure I Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 29 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 (a) DoF?, 1 , 2 ? EI 1 2EI 2 3EI [K], 1 1, 2 0 (remove all loading) EI 2EI 3EI 12 EI 12 3EI 1.333 EI L3 33 6 EI 6 3EI 2 : k12 2 EI 2 L 32 1 : k11 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 30 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 1 0, 2 1 C A ? EI B 2 2EI 3EI 3EI 4EI 3EI 3 2 EI 4 3EI 3 EI 6.2 EI L L L 5 3 3 6 EI 6 3EI 1 : k 21 2 EI 2 L 32 2 : k 22 k BC k BE k BA Hence: K EI k11 k 21 k12 1.333 2 EI 2 6.2 k 22 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 31 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 (b) [P], now include any loading which corresponds to the identified DoF. EI 2EI 3EI BOOM! 12kN - EXT (see Datasheet 2) M = 12 x 1.25 =15 kNm - EXT PIN, M=0 12kN - INT PIN, M = 0 15 kNm INT B B 5kN/m - EXT B +14.22 kNm INT W a2 b L2 32 2 2 1 M F BE 14.22 kNm 32 Wa 32 2 21.33 kN ab 3 M F BE -15.625 kNm INT B 21.33 kN (-ve to DELTA 1) INT b =1 32kN EXT M F BC M F BC wL2 1 wL2 5 52 5 52 12 2 12 12 2 12 15.625 kNm a=2 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 32 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 We REALLY need to understand the ‘difference’ between ‘internal’ and ‘external’ loading. P EXT INT Load in the direction of 1 ? EXT - INT P1 12 21.33 33.33 kN Or P1 0 12 21.33 33.33 kN Loading in the direction of 2 ? P2 15 15.625 14.22 16.405 kNm Or P2 0 15 15.625 14.22 16.405 kNm Hence: 33.33 kN P 16.405 kNm (c) The next step is to determine the actual DoF values, K 1P Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 33 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 1 6.2 EI 2 EI 33.33 1 1.33EI 6.2 EI 2 EI 2 EI 2 EI 1.33EI 16.4 2 1 1 4.246 EI 2 2 1 2 EI 33.33 6.2 EI 2 EI 1.33EI 16.4 6.2 EI 33.33 2 EI 16.4 4.246 EI 2 1 56.4 56.4 EI 10 103 1 5.64 10 3 m or 5.64 mm 2 2 EI 33.33 1.33EI 16.4 4.246 EI 2 1 20.84 20.84 EI 10 103 2 2.084 10 3 rads B A C B 2.084 10 4 1.042 10 3 rads 1 2 1 2 ‘Individual’ Beams Next, determine the ACTUAL Moments at B for each separate beam element, given the displacements evaluated above. Note the MF moments are for the being analysed NOT from the combined load vector! Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 34 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 M AB 0 PIN 3 F 2 B A M BA LBA 3 0 2 10 10 3 2 2.084 10 3 1.042 10 3 0 3 3 20.84 kNm 2 EI BA LBA M BA M BA M BA M CB 0 PIN 3 F 2 B C M BC LBC 3 0 2 2 10 10 3 3 3 2 2 . 084 10 1 . 042 10 15.625 5 5 25 15.625 9.38 kNm M BC M BC M BC M BE M BE M BE 2 EI BE LBE 3 F 2 B E M BE LBE 3 5.64 10 3 3 2 2.084 10 0 14.22 3 29.44 14.22 15.22 kNm 2 3 10 10 3 3 M EB M EB 2 EI BC LBC 2 EI EB 3 F 2 E B M EB LEB LEB 2 3 10 10 3 3 3 5.64 10 3 3 2 0 2.084 10 7.11 3 M EB 78.23 kNm NOTE: M F EB M F EB W a b2 L2 32 2 12 7.11 kNm 32 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 35 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 REACTIONS and BMD’s: A AB: B PIN, M = 0 +20.84 kNm BMD for AB VA R 6.95 kN -20.84 kNm R 20.84 kNm R 20.84 0 6.95 kN 3 R BC: 5kN/m - EXT +9.38 kNm PIN, M=0 B wL/2 = 5 x 5/2 =12.5 kN INT + R VC R 12.5 1.876 12.5 VC 14.376 kN +9.38 kNm R 9.38 0 1.876 kN 5 R 20.315 kNm =4.69+15.625 +9.38 kNm M FREE wL2 5 5 2 15.625 8 8 BMD for BC +ve M REACTIVE 9.38 4.69 2 BMD sign convention Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 36 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 37 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 38 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 1.25 -4.5 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 39 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 TUTORIAL 2 – MATRIX ANALYSIS OF STRUCTURES 1. Determine the loading vector [P] and total stiffness matrix [K] and draw the bending moment diagram. 15kN B A 5kN/m 5m 4 K 5 15 C 10m D 10m 10m 1 5 4 5 33.3 P 41.67 4 EI=10 MNm E 2. Determine the loading vector [P] and total stiffness matrix [K] and draw the BMD. EI = 104 kNm2. A 5kN/m B 14 K 10 4 10 5m P [62.5] 2EI 10m EI 3. 20kN Determine the loading vector [P] 2kN/m P [19.9] 4m 6m 4m 15m Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 40 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Past Exam Questions (10) Jan’11 (Dec’10) – Jan’20 MATRIX ANALYSIS Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 41 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 JANUARY 2020 (19-20) The structure ABCDEF shown in Figure Q1 has pin joint supports at A,D,E,F. Member BC has an off-set discrete vertical force of 20kN as shown. Member AB carries a uniformly distributed vertical load of 3kN/m acting along its length. All members have the relative flexural rigidities as indicated where EI is 1x103 kNm2. The solution should involve reference to DATASHEET Q1 as appropriate. i) Using the Displacement (Stiffness) method of matrix analysis and considering flexural deformation only, determine the stiffness matrix [K] for the structure. [7] ii) Determine the load vector [P] for the applied loading. [4] iii) Determine the displacements at B and C. [4] iv) Determine MBC, MCB and the Free, Reactive, and Combined Bending Moment Diagrams (BMD) for the beam element BC. [10] D 6m EI 4m 20kN 3m 3kN/m A B 3EI 2EI 4m EI EI Pin-joint C F E 4m Figure Q1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 42 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 JANUARY 2019 (18-19) The structure in Figure Q1 has pin joint supports at A and D and is fully fixed at C. Members BD and BC both have discrete forces of 20 kN acting at E and F respectively as shown. Member AB carries a uniformly distributed vertical load of 3 kN/m acting along its length. Members AB, BD and BC have the relative flexural rigidities as indicated where EI is 1x103 kNm2. The solution should involve reference to DATASHEET Q1 as appropriate. ii) Using the Displacement (Stiffness) method of matrix analysis and considering flexural deformation only, determine the stiffness matrix [K] for the structure. [8] ii) Determine the load vector [P] for the applied loading. [6] v) Determine the structural displacements at B. [4] vi) Determine the Bending Moment Diagram (BMD) for AB. [7] D Pin-joint 2m EI 20kN 4m F 20kN 3kN/m A 2EI E B 6m 1m EI C 3m Figure Q1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 43 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 JANUARY 2018 (17-18) The structure shown in Figure Q1 has a pin joint support at D and is fully fixed at A and G. Members BCE and EFG have a discrete central horizontal force of 20 kN at C and F respectively. Member DE carries a uniformly distributed vertical load of 3 kN/m acting along its length. All members have the relative flexural rigidities as indicated where EI is 1x103 kNm2. The solution should involve reference to DATASHEET Q1 as appropriate. iii) Using the Displacement (Stiffness) method of matrix analysis and considering flexural deformation only, determine the stiffness matrix [K] for the structure. [6] ii) Determine the load vector [P] for the applied loading. [5] vii) Determine the displacements at B and E. [4] viii) Determine the Bending Moment Diagram (BMD) for DE. [10] 4m B A EI 2m EI 20kN 4m C 3kN/m E D 2EI 6m F 20kN 4m Pin-joint EI 2m G Figure Q1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 44 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 JANUARY 2017 (16-17) The structure ABCD shown in Figure Q.1 has a pin jointed and sliding support at C and is fully fixed at D. Member AB is a cantilever beam with a discrete vertical load of 30 kN acting at A. Member BD carries a uniformly distributed load of 3 kN/m along its length. Member BC has a discrete off-centre vertical force of 50 kN as shown. All members each have the same flexural rigidity EI of 1x103 kNm2. The solution should involve reference to DATASHEET Q.1 as necessary. i) Using the Displacement (Stiffness) method of matrix analysis and considering flexural deformation only, determine the stiffness matrix [K] for the structure. [6] Determine the load vector [P] for the applied loading. [5] Determine the displacements at B. [4] Determine the vertical reaction at C, and the bending moment diagram (BMD) for member BC. [10] ii) iii) iv) 3m 2m 30kN A 4m 6m 50kN B C pin-jointed and slider connection 3kN/m D Figure Q.1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 , Page 45 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 JANUARY 2016 (15-16) The structure ABCDEF shown in Figure Q.1 has a pin joint support at A and D, while at E and F the structure is fully fixed. Member AB carries a uniformly distributed load of 10kN/m along it’s length. Member BC has a discrete mid-span vertical force of 100kN as shown. Member CD carries an off-centre discrete load of 180kN. All members each have the same flexural rigidity EI of 105 kNm2. (i) Using the Displacement (Stiffness) method of matrix analysis and considering flexural deformation only, determine the stiffness matrix [K] for the structure. [5] (ii) Determine the load vector [P] for the applied loading. [6] (iii) Determine the displacements at B and C. [4] (iv) Determine the vertical reaction at D, and the Bending moment diagram (BMD) for CD. [10] pin-jointed connection E 180kN 100kN 10kN/m 6m C A D B 6m 8m 6m pin-jointed connection F 12 m 12 m 10 m Figure Q.1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 46 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 JANUARY 2015 (14-15) The frame shown in Figure Q.1 has a sliding pin joint support at D and E, while at C the structure is fully fixed. Member BC carries a uniformly distributed load of 12kN/m along it’s length. Member BD has a discrete mid span horizontal force of 20kN as shown. The non-structural cantilever overhang AB carries a discrete load of 15kN and the sliding support at E experiences a vertical load of 70kN. All members each have the same flexural rigidity EI of 104 kNm2. (ii) Using the Displacement (Stiffness) method of matrix analysis and considering flexural deformation only, determine the stiffness matrix for the structure. [6] (ii) Determine the load vector for the applied loading. [6] (v) Determine the displacement of B and the reactions at pistons D and E. [13] D Sliding support with pin-jointed connection 20 kN 3m 12kN/m Cantilever beam AB A C B 1.1m 6m 15kN 3m E 70kN , Figure Q.1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 47 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 JANUARY 2014 (13-14) The frame ABCDEF shown in Figure Q.1 is rigidly fixed at A and pin joint supported at D. Horizontal motion is prevented by means of a tie bar FB which is pin jointed at both ends and attaches to the structure at B. The structural members AB, BC and BE are continuous and rigidly connected at B. The relative flexural rigidities are as indicated where EI is 10MNm2. Considering flexural deformation only and using the Displacement (Stiffness) method of matrix analysis and using DATASHEET Q.1, determine: (a) The stiffness matrix [K] for the structure. [6] (b) The loading vector [P]. [4] (c) The displacements at B and C [5] (d) The load acting in the tie bar FB. [10] 10m D E 20kN 5m 6 kN/m 2m F 2EI B EI 3EI C 15kN 5m 2.5m A Figure Q.1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 48 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 DECEMBER 2012 (12-13) The frame structure ABCDE shown in Figure Q.1 is rigidly fixed at A, D and E. Members BE and CD carry a uniform distributed load of 2kN/m. Member BC has a 20kN load acting horizontally at mid-span. The relative flexural rigidities of each member are as shown in Figure Q.1, where EI is 10MNm2. Considering flexural deformations only, and making use of the supplied DATASHEET Q.1, determine: i) the stiffness matrix [K] for the structure; ii) the loading vector [P] for the structure; [5] [5] iii) the displacements at B and C; [5] iv) all reactions acting at D; [5] v) the Bending Moment Diagram (BMD) for member CD. [5] 10 m 2kN/m 4EI C 2.5 m 5m D EI 20kN 2kN/ m EI B 2EI E 5m A 5m Figure Q.1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 49 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 DEC 2011 (11-12, NEW TRIMESTER SYSTEM) The frame structure ABCDEF shown in Figure Q.1 is pin supported at A, fully fixed at C and F and has a pin joint support at E. Member AB carries a discrete force of 10kN at the position shown, member CD carries a uniformly distributed load of 6kN/m and a discrete force of 24kN is applied to DE at mid-span. The members each have their relative flexural rigidities as indicated, where EI is 10MNm2. Determine: (a) the stiffness matrix [K] for the structure using the Displacement (Stiffness) method of matrix analysis and considering flexural deformation only; [6] ii) the load vector [P] for the applied loading; [6] iii) the displacements at D and E; [4] iv) the bending moment MDE, the reactions at E, and sketch the bending moment diagram for portion DE. [9] Note: Use may be made of DATASHEET Q.1 10 kN B A 2EI EI 4m 6 kN/m C 24kN D 2EI E 2EI 4m EI F 4m 3 m 3 m 6m 10m Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Figure Q.1 Page 50 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 Q.1 DEC 2010 (10-11, NEW TRIMESTER SYSTEM) The frame ABCDE shown in Fig.Q.1 is rigidly supported at A, simply supported at D, and carries uniformly distributed loading of 12kN/m and 6kN/m along members AB and BD respectively. A horizontal discrete force of 16kN is also applied at point C on member BD and a vertical discrete force of 10kN acts at E. The frame members have their relative flexural rigidities as shown, where EI is 104 kNm2. (a) Using the Displacement (Stiffness) method of matrix analysis and considering flexural deformation only, determine the stiffness matrix [K] for the structure. [6] (b) Determine the load vector [P] for the applied loading. [6] (c) Determine the displacements at B and the reaction at support D. [13] Note: Use may be made of DATASHEET Q.1 10kN 12kN/m 6kN/m 16kN Figure Q.1 Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 51 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 TYPICAL DATASHEET page 1 of 2 -6EI/L2 6EI/L2 2EI/L 4EI/L 6EI/L2 -6EI/L2 4EI/L 2EI/L -12EI/L3 12EI/L3 -6EI/L2 12EI/L3 -12EI/L3 6EI/L2 6EI/L2 3EI L3 -3EI L2 3EI L3 3EI L2 3EI L -6EI/L2 3EI L2 3 2 1 2 2L M Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 3EI L L Page 52 Dr David R Gordon, Matrix Analysis, Level 4, 2020/21 DATASHEET page 2 of 2 (contd.) (FIXED END MOMENTS) w wL2/12 -wL2/12 wL/2 wL/2 W WL/8 -WL/8 W/2 W/2 W Wa2b/L2 -Wab2/L2 Wb/(a+b) Wa/(a+b) B A F M AB 21 M FBA M AB 2EI 3 F 2 1 2 M AB L L Dr David R Gordon, ED&A4 Trimester 1 Session 2020-21 Page 53