1. Introduction
The base plates correspond to one of the most frequent column connections of steel structures. These connections are responsible for transferring loads from the superstructure to the foundations. However, the performance of these connections was deficient during recent seismic events in the USA and Japan, where significant damage and failure of these joint elements was reported [
1,
2].
An exposed column base consists of several components, such as: column sections, base plate, stiffeners, anchor rods, concrete foundation and shear-lug. Each of these components affects the connection’s capacity to withstand axial load, shear load and bending moments. Current design methods, such as those presented in the AISC Steel Design Guide 1 [
3], provide design procedures that allow for sizing of the base plate of exposed columns and their anchor rods. However, these design methods do not consider combined failure mechanisms, such as those observed in several experimental studies [
4], resulting in non-conservative designs. In other cases, as the current guidelines do not consider joint configurations with stiffeners, the design often specifies plates with thicknesses that is not commercially available [
5].
Numerical studies using finite elements indicate that the base plates designed using the current guidelines do not behave as expected, leading to premature crushing of concrete when using base plates with thickness higher than 25 mm [
6]. A recent experimental study on exposed base plates considering axial load and bending moment [
7] showed an important correlation between the thickness of the base plate and the performance of the connection. This study concludes that despite complying with the design guidelines, flexural capacity may not be reliable due to plate interaction with other components such as the anchors. On the other hand, few studies have addressed the behavior of column bases with stiffened base plates, which are very common in the practices of detailing and construction of steel structures, as it allows for reducing the thicknesses of base plates [
8,
9]. However, there are no numerically or experimentally validated design procedures that consider the different performance of stiffened and non-stiffened base plates. The response of connections in terms of stiffness, strength, rotational capacity and energy dissipation is heavily dependent on the details of connection and, therefore, on the components considering their location and individual strength [
10]. These problems could be alternatively solved by improving material properties or by the use of novel nanostructured materials, which have emerged to allow the synergy of high strength and high ductility modifying failure mechanisms [
11]. However, it is usually preferred an engineering and constructive solution, using currently commonly used materials.
The exposed and embedded base plate connection have been researched by [
12,
13,
14,
15], obtaining that rotational fixity of base plate in steel moment resisting frames strongly influences their seismic response. However, the stiffened base plates were not considered by this investigation.
In this investigation, a numerical study on the behavior of stiffened and non-stiffened base plates is carried out, considering the contribution of different components to each configuration. The aim of the research is to evaluate numerically the failure mechanisms in stiffened and non-stiffened base plates. Additionally, due to currents design methods are focused in non-stiffened base plates a new design method is proposed. The numerical study was conducted using finite element models considering material, geometric and contact nonlinear properties. Axial load and bending moment were simultaneously applied with the goal of identifying the behavior of the base plate and its interaction with the stiffeners and anchor rods. The welds were designed to remain within the elastic range and to develop the inelastic behavior of the connected elements, being considered as ideal monolithic contacts in the numerical models. Similarly, concrete was designed to remain elastic. These conditions are like those observed on typical connection tests that intend to evaluate the seismic performance of the links, avoiding a fragile failure of elements with limited inelastic capacity, such as, welding and concrete. In the final part of the paper, the authors propose a new design method based on yield lines theory, suitable to design base plates with stiffened and not stiffened configurations.
Author Contributions
Conceptualization, E.N.; Methodology, E.N.; Investigation, H.D. and E.N.; Writing—original draft, E.N. and C.O.-V.; Writing—review and editing, E.N. and C.O.-V.; Funding acquisition, E.N.; Resources, E.N.; Supervision, E.N. and C.O.-V. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Conflicts of Interest
The authors declare no conflict of interest.
References
- Grauvilardell, J.; Lee, D.; Hajjar, J.; Dexter, R. Synthesis of Design, Testing and Analysis Research on Steel Column Base Plate Connections in High-Seismic Zones; Structural Engineering Report, No. ST-04-02. Technical Report; Department of Civil Engineering, University of Minnesota: Minneapolis, MN, USA, October 2005. [Google Scholar]
- Fahmy, M. Seismic Behavior of Moment-resisting Steel Column Bases. Ph.D. Thesis, Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, USA, 2000. [Google Scholar]
- Fisher, J.M.; Kloiber, L.A. Steel Design Guide Series 1–Base Plate and Anchor Rod Design, 2nd ed.; American Institute of Steel Construction: Chicago, IL, USA, 2006. [Google Scholar]
- Gomez, I.; Kanvinde, A.; Smith, C.; Deierlein, G. Exposed Column Base Connections Subjected to Axial Compression and Flexure; Technical Report; American Institute of Steel Construction, AISC: Chicago, IL, USA, August 2010. [Google Scholar]
- Kanvinde, A.; Jordan, S.; Cooke, R. Exposed column base plate connections in moment frames—Simulations and behavioral insights. J. Constr. Steel Res. 2013, 84, 82–93. [Google Scholar] [CrossRef]
- Lee, D.; Goel, S.; Stojadinovic, B. Exposed column-base plate connections bending about weak axis: I. Numerical parametric study. Int. J. Steel Struct. 2008, 8, 11–27. [Google Scholar]
- Lim, W.; Lee, D.; You, Y. Exposed column-base plate strong-axis connections for small-size steel construction. J. Constr. Steel Res. 2017, 137, 286–296. [Google Scholar] [CrossRef]
- Blodgett, O. Design of Welded Structures; The James F. Lincoln Arc Welding Foundation: Cleveland, OH, USA, 1966; Volume 3.3, pp. 1–32. [Google Scholar]
- Karbakhsh, A.; Bin, I.; Binti, Z. Finite element analysis of bolted column base connection without and with stiffeners. Int. J. Phys. Sci. 2011, 6, 1–7. [Google Scholar]
- Latour, M.; Rizzano, G. Mechanical modelling of exposed column base plate joints under cyclic loads. Eng. Technol. 2019, 162, 105726. [Google Scholar] [CrossRef]
- Tian, L.; Li, L. A Review on the Strengthening of Nanostructured Materials. Int. J. Curr. Eng. Technol. 2018, 8, 236–249. [Google Scholar] [CrossRef] [Green Version]
- Myers, A.; Kanvinde, A.; Deierlein, G.; Fell, B. Effect of weld details on the ductility of steel column baseplate connections. Eng. Technol. 2009, 65, 1366–1373. [Google Scholar] [CrossRef]
- Grilli, D.; Kanvinde, A. Embedded column base connections subjected to seismic loads: Strength model. J. Constr. Steel Res. 2017, 129, 240–249. [Google Scholar] [CrossRef]
- Torres, P.; Zareian, F.; Kanvinde, A. A hysteretic model for the rotational response of embedded column base connections. Soil Dyn. Earthquake Eng. 2018, 115, 55–65. [Google Scholar] [CrossRef]
- Falborski, T.; Hassan, A.; Kanvinde, A. Column base fixity in steel moment frames: Observations from instrumented buildings. J. Constr. Steel Res. 2020, 168, 1–13. [Google Scholar] [CrossRef]
- A36/A36M-19. Standard Specification for Carbon Structural Steel; Philadelphia American Society for Testing and Materials: Philadelphia, PA, USA, 2019. [Google Scholar]
- A193/A193M-17. Standard Specification for Alloy-Steel and Stainless Steel Bolting for High Temperature or High Pressure Service and Other Special Purpose Applications; American Society for Testing and Materials: Philadelphia, PA, USA, 2017. [Google Scholar]
- ACI Committee 318-14. Building Code Requirements for Structural Concrete and Commentary; ACI Committee: Farmington Hills, MI, USA, 2014. [Google Scholar]
- Ansys Inc. ANSYS Multiphysics 16.0; Ansys Inc.: Canonsburg, PA, USA, 2015. [Google Scholar]
- Gomez, I.; Kanvinde, A.; Smith, C.; Deierlein, G. Shear Transfer in Exposed Column Base Plates; Technical Report for American Institute of Steel Construction; American Institute of Steel Construction: Chicago, IL, USA, 2006. [Google Scholar]
- Ghassemieh, M. Evaluation of Stiffened End-Plate Moment Connection through Optimized Artificial Neural Network. J. Software Eng. Appl. 2012, 5, 156–167. [Google Scholar] [CrossRef]
- Bae, S.; Bayrak, O.; Jirsa, J.; Klingner, R. Anchor Bolt Behavior in ASR/DEF-Damaged Drilled Shafts; Technical Report N IAC 88-5DDIA004; Report for the Texas Department of Transportation, University of Texas at Austin: Austin, TX, USA, 2007. [Google Scholar]
- Desayi, P.; Krishnan, S. Equation for the stress-strain curve of concrete. J. Am. Concr. Ins. 1964, 61, 345–350. [Google Scholar]
- Gere, J.; Timoshenko, S. Mechanics of Materials, 3rd ed.; PWS-KENT Publishing Company: Boston, MA, USA, 1990. [Google Scholar]
- EN1993 Eurocode 3. Design of Steel Structures; Comité Européen de Normalisation (CEN): Brusels, Belgium, 2003. [Google Scholar]
Figure 1.
Specimen configurations.
Figure 2.
Finite element models for each specimen configuration.
Figure 3.
Constitutive models considered for (a) ASTM-A36 steel, (b) ASTM-A193 steel and (c) concrete.
Figure 4.
Loading protocol and response parameters.
Figure 5.
Influence of base-plate thickness model UBP-1.
Figure 6.
Influence of the anchor rods configuration.
Figure 7.
Influence of the stiffener configuration.
Figure 8.
Comparison of FEM results with estimations of the triangular stress block (TSB) method.
Figure 9.
Comparison of FEM results with estimations of the rectangular stress block (RSB) method.
Figure 10.
Comparison of FEM results with estimations of the component method (CM).
Figure 11.
Comparison of flexural strength estimations of the different methods with FEM results for non-stiffened base plates.
Figure 12.
Comparison of flexural strength estimations of the proposed method with FE models results for stiffened base plates.
Table 1.
Simulations matrix.
Model | tp (mm) | g (mm) | ts (mm) | dr (mm) | Fur (mm) |
---|
UBP-1-1 | 19 | N/A | N/A | 22 | 408 |
UBP-1-2 | 25 | N/A | N/A | 22 | 408 |
UBP-1-3 | 38 | N/A | N/A | 22 | 408 |
UBP-1-4 | 19 | N/A | N/A | 22 | 878 |
UBP-1-5 | 25 | N/A | N/A | 22 | 878 |
UBP-1-6 | 38 | N/A | N/A | 22 | 878 |
UBP-2-1 | 25 | 210 | N/A | 22 | 408 |
UBP-2-2 | 25 | 390 | N/A | 22 | 408 |
UBP-2-3 | 25 | 210 | N/A | 22 | 878 |
UBP-2-4 | 25 | 390 | N/A | 22 | 878 |
SBP-1-1 | 19 | N/A | 10 | 22 | 408 |
SBP-1-2 | 19 | N/A | 10 | 22 | 878 |
SBP-2-1 | 19 | N/A | 10 | 22 | 408 |
SBP-2-2 | 19 | N/A | 10 | 22 | 878 |
SBP-3-1 | 19 | N/A | 10 | 22 | 408 |
SBP-3-2 | 19 | N/A | 10 | 22 | 878 |
Table 5.
Limit states that control the design of base plate type SBP-2.
LS1 | | |
|
LS2 | Idem to SBP-1 |
LS3 | Idem to SBP-1 |
LS4 | Idem to SBP-1 |
LS5 | Idem to SBP-1 |
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