Research, Development, and Practice in Structural Engineering and Construction Vimonsatit, V., Singh, A., Yazdani, S. (eds.) ASEA-SEC-1, Perth, November 28–Decmber 2, 2012
DESIGN OPTIMIZATION OF INDUSTRIAL PORTAL FRAME WITH OVERHEAD CRANES Mehdi Shokouhian1 and Reza Sadeghi2 1
Department of Civil Engineering, Tsinghua University, Beijing, China E-mail:
[email protected] 2 Bryant Concepts Pty Ltd, U3 66 Rundle St, Kent Town, SA 5067, Australia E-mail:
[email protected]
Portal frames are the most commonly used structural forms for single-storey industrial structures. For structures of this type, an unsuitable layout plan can increase total cost of construction; hence a suitable layout plan is of importance to achieve an economical design. This may require several trial designs. The optimization study presented here examines some key geometric and material parameters of industrial portal frame structures with different over head cranes capacities. The key parameters considered herein are: span of portal frame, portal frame spacing, overhead crane capacity and material properties of the single and double bay portal frames. The internal forces and deflections are calculated under the applicable gravity (considering the action of both crane and its load) by using elastic first-order static analyses, utilizing the finite element method. The current study examines the function of each of the above-mentioned parameters and presents the optimum parameters in terms of weight per unit area of portal frame. The results are presented in graphical form suitable for the preliminary stages of design of industrial portal frame structures with overhead cranes.
Keywords: Portal frame, optimization, Industrial building, Steel structures, Geometric and material effects, Overhead cranes.
1
Introduction
Single-storey steel portal frames offer a cost effective form of structure for most singlestorey buildings where a large, open space is required. These types of structures can be used for industrial, airplane hangars, storage facility and the like. The major components of a portal frame building are a series of parallel portal frames which are placed at a 1
regular spacing. The economy of the structure is generally affected by the requirements for spans and the spacing of the frames. Planning column locations to avoid interference with any equipment, fulfilling the functional requirements of the building and minimizing the building layout plan to achieve a low cost solution is of importance.
Design optimization of Portal Frames with Overhead Cranes M. Shokouhian, R. Sadeghi
2
Background
Extensive studies on the structural cost of single-storey buildings have been carried out by Horridge and Monis in 1986. Gurlement et al, 2001, presented a practical method for single-storey steel structure, using a discrete minimum weight and Eurocode design. In 2003, Kamal et al, carried out a weight optimization of two-hinged steel portal frames under multiple loadings. Kravanja and Zula, 2009, presented the simultaneous cost, topology and standard cross-section optimization of single storey industrial steel building structures employing the mixedinteger non-linear programming approach. Liu Feng et al performed an optimization study on the economical dimensions and optimum design of portal frames, both without cranes and with light cranes. This study follows their works and performs a cost optimization study on portal frames with a range of crane capacities from light to medium capacity. The results presented herein can be used in the preliminary stages of the design of industrial portal frame structures with overhead cranes. 3
350 MPa steel grades which are two common steel grades in the construction of this type of structures. The soil is also assumed to have a conventional load bearing capacity and the cost of footing design is not considered in this study. The cost optimization of portal frame building on low bearing soils is not within the scope of this paper as the cost optimization may be greatly affected by the geotechnical properties of the soil and consequently the selection of clear span and portal spacing may be governed by accounting the bearing capacity of the soil.
Problem Definition and Assumptions:
The cost optimization of a industrial portal frame is a function of diverse parameters such as: the framing system (tapered girder, portalized roof truss, lattice column etc), the span of the frames, the spacing between the portal frames, the pitch of the roof, different steel grades, different gravity loads (dead, live and snow loads), lateral loads (wind and earthquake), load combinations. Simplification of the problem indicates that the most significant parameters are: the span of portal frame, portal frames spacing (distance between the frames), overhead crane capacity and material properties. This study focus of the effect of above mentioned parameters in single and double bay portal frames for light and medium overhead capacity cranes ranging from 5 to 60 ton. The steel materials considered herein, are 250 and 2
Figure 1 Portal frame configuration (a) single bay (b) multi bay
Considered in this study is a zero-pitched (flat roof) portal frame with a built up tapered section rafter and lattice column system, designed to carry the gravity loads of cranes, dead, live, and snow loads. The geometry of the lattice column is constructed from hot rolled universal beam (UB) or universal column (UC) sections and light-gauge steel is used for cladding. A distributed load including a gravity load of the purlins and cladding, a live load together with a snow load equaling 2 KPa is assumed on the roof. The cranes load is as per AS1418, Cranes, hoist and winches. The effect of lateral forces such as wind and seismic has been ignored. The
Research, Development, and Practice in Structural Engineering and Construction Vimonsatit, V., Singh, A., Yazdani, S. (eds.) ASEA-SEC-1, Perth, November 28–Decmber 2, 2012
summary of geometric parameters considered in this study is shown in table 1. Table 1. Geometric Parameters of Portal Frame Crane Capacity Span frame spacing tonne (m) (m) 5 10 5 20 15 6 40 20 7 60 25 8 30 9 35 10 12
As shown in table 1, the portal frame spacings of 5,6,7,8,9,10 and 12m are considered for crane ranging from 5 to 60 ton for a 20m span portal frame. Single span, Span=20m 120
5t 20t 40t 60t
2
Weight per unit area(kg/m )
110
Structural modeling and design
100
90
80
70
60 4
5
6
7
8
9
10
11
12
13
Double Span=20m Portal span, Frame Spacing (m)
(2-a)
100
2
The internal forces and deflections are calculated under the applicable gravity loads (crane, dead, live and snow) by using the elastic first-order static analysis, utilizing Strand7, finite element analysis software. To achieve a cost-effective design, the nominal bending moment and axial force are considered as close as possible to the section capacity of the member. Based on the extracted actions and deflections, structural members have been designed manually in accordance with AS4100-1998 Steel Structures.
Weight per unit area(kg/m )
4
5.1 Effect of portal frame spacing:
5t 20t 40t 60t
90
80
70
60
50 4
5
6
7
8
9
10
11
12
13
14
(2-b)
Portal span, Frame Spacing (m) Single Span=30m 120
5
Results and Discussion: 5t 20t 40t 60t
3
2
Weight per unit area(kg/m )
110
There are numerous possible cases of the span width and the spacing between the portal frames, for a given crane capacity. To achieve optimum values of these parameters, some simplification is required: after extracting the optimum value of a given parameter and assuming it as a constant, the effect of other parameters are investigated and their optimum values are obtained. Finally the results based on the defined parameters are presented in terms of weight of the steelworks per unit area of the building.
100
90
80
70 4
5
6
7
8
9
10
11
Portal Frame Spacing (m)
12
13
14
(2-c)
Figure 2- Optimal Frame Spacing Span (a) a 20m single-bay (b) a 20m double-bay portal frame (c) 30m span single-bay.
Design optimization of Portal Frames with Overhead Cranes M. Shokouhian, R. Sadeghi
Based on the results presented in section 5.1, and taking the spacing of the frames 7m, as a constant, the optimum span of single and double-bay portal frames are investigated and results are shown in span, figure 3.a and 3.b. Single L=7m
A relative weight comparison between a double and single-bay portal frame with several various spacings between the frames are shown for different crane capacities in figures 4a to 4d. Generally, the weight difference between double and Span=20m, 5t Crane 75
70
5t 20t 40t 60t
110
2
60
55
Single-bay Double-bay
4
5
6
7
8
9
10
11
12
13
(4-a)
Portal Frame spacings 90
Span=20m, 20t Crane
85
80 80
70
2
60 10
15
20
25
30
35
40
Double Span(m) span, L=7m
(3-a)
110
5t 20t 40t 60t
100 2
75
70
65
Single-bay Double-bay
60
90
4
5
6
7
8
9
10
11
12
13
(4-b)
Portal frame spacing 80
Span=20m, 40t Crane
100
70 95
60 2
Weight per unit area(kg/m )
Weight per unit area(kg/m )
65
50
100
Weight per unit area(kg/m )
Weight per unit area(kg/m )
120
5.3 Comparison between spacing in single and double–bay portal frames
2
5.2 Effect of span of a portal frame
ton crane in double-bay portal frame. As shown, the optimal span increases when a higher crane capacity is used.
Weight per unit area(kg/m )
As shown in figures 2a and 2b, in most cases, 7m spacing between portal frames is the most economical spacing for a given overhead crane. Horridge and Morris (1986) in their paper concluded that, 7.5m is the most economical spacing for a portal frame spanning over 20m. To be sure about the results, a 30m span portal frame is also considered and results as shown in figure 2.C indicate that 7m is the optimal portal spacing. The optimal spacing is more evident for higher capacity cranes or wider span.
50 10
15
20
25
Span(m)
30
35
40
(3-b)
Figure 3- Optimum span for portal frame (a) singlebay (b) double-bay portal frame.
For example, a 25m span is the optimum span for 60 ton crane in both single and double-bay portal frame and 15m is the optimal span for 5 4
90
85
80
Single-bay Double-bay
75
70 4
5
6
7
8
9
10
Portal frame spacing (m)
11
12
13
(4-c)
Research, Development, and Practice in Structural Engineering and Construction Vimonsatit, V., Singh, A., Yazdani, S. (eds.) ASEA-SEC-1, Perth, November 28–Decmber 2, 2012 Portal frame spacing 7m - 20t Crane
Span=20m, 60t Crane 90
120 115
2
Weight per unit area(kg/m )
2
Weight per uni area(kg/m )
85
110 105 100 95 90
Single-bay Double-bay
85
80
75
70
Single-Bay Double-Bay
65
60
80 4
5
6
7
8
9
10
11
12
10
13
15
20
25
30
(5-b)
105
2
Weight per unit area (kg/m )
100
single bay portal frames reduces when the spacing changes relative to the optimum portal spacing. This means using a doublebay portal frame over a single-bay portal frame is the most justifiable at the optimum portal spacing where the largest weight difference is evident.
95
90
85
80
Single-bay Double-bay
75
70 10
15
20
25
35
(5-c)
Portal frame Spacing 7m - 60t Crane Single-Bay Double-Bay
2
Weight per unit area (kg/m )
120
Similar to section 4.3, a relative weight per unit area difference between single and double-bay configuration are shown in figures 5a to 5d. Generally, the weight difference between double and single bay portal frames reduces when the span increases relative to the optimum portal span. This means using a double-bay portal frame over a single-bay portal frame is the most justifiable at the optimum span where the largest weight difference is evident.
30
Span (m)
5.4 Comparison between spans of a portal frame in single and double bay portal frames 110
100
90
80
10
15
20
25
Span (m)
30
35
(5-d)
Figure 5 - Effect of span of portal frames for different crane capacity
Portal frame spacing 7m - 5t Crane
85
80 2
40
Portal frame spacing 7m - 40t Crane
Figure 4- Effect of span of a portal frame in single and double-bay portal frames
Weight per unit area (kg/m )
35
Span (m)
(4-d)
Portal frame spacing (m)
5.5 Effect of material
75
A steel material with yield strength ranging between 250 and 350 MPa are considered in this study. This is the range of the steel that most steelworks are done. Figure 6 and 7 show the effect on optimized weight of a portal frame. As it
70
65
60
55
Single-bay Double-bay
50 10
15
20
25
Span (m)
30
35
(5-a)
5
Design optimization of Portal Frames with Overhead Cranes M. Shokouhian, R. Sadeghi
4- The weight difference between double and single-bay portal frames reduces when either the span or portal spacing changes relative to their optimum values. This means using a double-bay portal frame over a single-bay portal frame is the most justifiable at the optimum span where the largest weight difference is evident.
is evident, using different steel grades, the extremums in either of the diagrams follow a similar pattern. It is recommended to use higher steel grades for higher crane capacities. Portal frame spacing 7m - 20t Crane 90
2
Weight per unit area (kg/m )
85
References
80
75
Journal Papers
70
Fy=250 MPa Fy=350 MPa
65
10
15
20
25
30
35
Span(m)
Figure 6- Effect of steel grades for different span – 20t crane Portal frame spacing 7m - 60t Crane
2
Weight per unit area (kg/m )
120
Fy=250 MPa Fy=350 MPa
110
100
90
80
70 10
15
20
25
30
35
Span(m)
Figure 7- Effect of steel grades for different span – 60t crane
4
Results:
This study focuses on the optimum geometric and material properties of an industrial portal frame with light to medium overhead crane. These results to be presented are as follow: 1- In most cases, 7m is the optimal spacing between the portal frames for single and double bay portal frames. 2- Optimum span of a portal frame increases when a higher crane capacity is used. 3- It is recommended to use higher steel grades for structural members when higher crane capacities are utilized.
6
Feng L., Bing G., Changbing C., Gang D. Economical Dimensions and Optimum Initial Design of Portal Frame, Steel construction (Chinese) Journal 2003(1). Vol 18, No.63 Kamal OA, El-Mahdy OO, El-Komy GA. Optimum design of one-bay portal steel frames. J Eng Appl Sci 2003:723–41. Kravanja. S , Zula.T, Cost optimization of industrial steel building structures Advances in Engineering Software Management, Elsevier, 41 (2010) 442–450, April , 2009. Gurlement G, Targowski R, Gutkowski W, Zawidzka J, Zawidzki J., Discrete minimum weight design of steel structures using EC3 code. Struct Multidisc Optim 2001;22:322–7 Books Woolcock S., Kitipornchai S., Bradford. M. A., G.A. Haddad, Design of Portal Frame Buildings Including Crane Runway Beams and Monorails, 4th ed., Australian Steel Institute Sydney Australia 2011. King C.M, Design of Steel portal frames for Europe, The Steel Construction Institute, Silwood Park, Ascot, Berkshire, SL5 7QN AS4100-1998 Steel structures, STANDARDS AUSTRALIA, ISBN 0 7337 1981 3 AS1418 Cranes, hoists and winches, STANDARDS AUSTRALIA Proceeding Papers HORRIDGE, J.F. and MORRIS, L.J. Single Story Building Cost Considerations, Pacific Structural Steel Conference, New Zealand Heavy Engineering Research Associations Aug 265285,1986
