Analysis of Selected Methods of Machine Seating using Multi-Bolted
Foundation Connections
RAFAŁ GRZEJDA
Faculty of Mechanical Engineering and Mechatronics,
West Pomeranian University of Technology in Szczecin,
19 Piastow Ave., 70-310 Szczecin,
POLAND
Abstract: - Finite element modeling of multi-bolted foundation connections applied in the case of seating of
heavy machines or devices is reported. Connections performed by means of 3 different types of chocks were
investigated. Characteristics of stiffness for the assumed models of multi-bolted foundation connections at the
assembling phase were outlined and discussed. Conclusions of great relevance to engineering design were
presented.
Key-Words: - machine seating, multi-bolted foundation connections, foundation chocks, assembly, pre-tension,
FE analysis.
Received: April 7, 2024. Revised: August 16, 2024. Accepted: September 18, 2024. Published: November 15, 2024.
1 Introduction
In the engineering industry, it is repeatedly
necessary for machines to have a proper foundation,
without which their correct operation is not possible.
Correctly sited machines can determine the
operational safety of entire production lines, their
durability, the absence of vibration, the proper
functioning of bearings, as well as the safety of the
people working on the production site, [1], [2], [3].
The seating of heavy machines or devices on
foundations is commonly achieved using multi-
bolted connections, which as a rule must be pre-
tensioned, [4], [5]. As a result of various factors
(including geometric imperfections of flanges), the
surfaces of the components to be joined do not
adhere tightly to each other, [6], [7]. To enable
machines and devices to be installed, special
foundation chocks are used in such connections.
There are 3 types of these chocks, [8], [9], [10]:
• steel chocks (SCs),
• polymer chocks (PCs),
• polymer-steel chocks (PSCs).
The earliest known method of machine seating
is that in which SCs (mainly rigid chocks, but also
wedge chocks and adjustable chocks, [11]) are used.
This seating is associated with two inconveniences
when assembling the multi-bolted foundation
connections (MBFCs). The first is the necessity to
guarantee an even distribution of contact pressure
on all chocks by matching their surfaces to the
retaining surfaces of the machine being assembled
and the foundation. Such measures are challenging,
and time-consuming. Furthermore, in this case of
seating, applying the preload of the foundation bolts
causes significant contact deformations between the
components to be joined, [9].
The second method of machine seating is the
seating on cast PCs. With this method, precise
machining surfaces of the components to be joined
is not necessary. Moreover, the direct casting of the
chocks underneath the machine base ensures that the
joined surfaces of these components adhere closely
together. Unevenness due to the roughness of the
joined surfaces is infilled with polymer, making the
pressure distribution on these surfaces more
beneficial than when seated with SCs, [12]. But the
drawback of seating on PCs is that they creep under
operational conditions, causing pre-tension
relaxation in the foundation bolts, [8], [13].
The third and most recent method to perform
machine seating is polymer-steel chock seating. It
combines the strengths of seating under the two
above-mentioned methods and minimizes the
shortcomings occurring there. In connections made
with PSCs, chock creep is significantly reduced. At
the same time, the abutment surfaces of the joined
components fit tightly together and there is no need
to adjust them. Additionally, with this type of multi-
bolted foundation connection, SCs with identical
thickness can be used throughout the connection
area.
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MBFCs often have a considerable influence on
the vibration, dependability, and sustainability of
whole mechanic systems. Thus, knowledge of their
behavior under assembly and operating conditions is
required to analyze the problems they present. To
find out about this behavior, the corresponding
stiffness characteristics are usually specified.
Investigations concerning MBFCs with steel and
PCs are reported in [14] and [15], among others. On
the other hand, investigations of foundation multi-
bolted connections with PSCs are provided, for
instance, in [8], [11]. The present article is a further
study of foundation multi-bolted connections, with
the main purpose of determining the stiffness
characteristics of the components joined during the
assembly of the multi-bolted foundation connection
for all its types mentioned above, including steel,
polymer, and polymer-steel chocks.
The subjects of this study are symmetrical
segments of a multi-bolted foundation connection
formed by two rectangular slabs and a rectangular
chock placed between the slabs. It was assumed that
the chock could be of any of the 3 types mentioned
above. Layoutsseparated in this way were modeled
using the finite element method (FEM) in order to
obtain characteristics of the stiffness of the joined
components in the state of assembly. EPY resin,
[16], [17], was chosen as the polymer chock
material. The study resulted in findings of great
relevance to engineering design.
2 Fundamentals of Research
One of the major issues addressed in the
computations of MBFCs concerns the stiffness
analysis of their components. Regarding bolts to be
linear elements, their elastic flexibility can be
defined either with the guidelines provided in VDI
2230, [18] or with a simplified method, [19]. There
is no similarly simple method to identify the elastic
flexibility of components joined in MBFCs. For this
reason, FEM is normally used to specify it
accurately.
For analyzing the aforementioned seating
methods, computations were made for the models
labeled as:
• FEM-S – FE-based model that uses the steel
chock,
• FEM-P – FE-based model that uses the polymer
chock,
• FEM-PS – FE-based model that uses the
polymer-steel chock.
This article investigates a segment of a multi-
bolted foundation connection, with the dimensions
of a single joint illustrated in Figure 1, Figure 2 and
Figure 3. The single joint was formed with a pair of
steel slabs (2) and (4) representing segments of the
base of the machine and the ground footing. A
chock (3) or (6) was placed between the slabs,
appropriate to the seating method used. As the aim
of this article was to analyse the stiffness of the
joined components, the full model of the bolt was
not considered in the connection.
Fig. 1: Dimensions of the FEM-S model: 1 – upper-
pressure punch, 2 – upper slab, 3 – steel chock, 4 –
lower slab, 5 – lower pressure punch
Fig. 2: Dimensions of the FEM-P model: 1 – upper-
pressure punch, 2 – upper slab, 4 – lower slab, 5 –
lower pressure punch, 6 – polymer chock
Fig. 3: Dimensions of the FEM-PS model: 1 – upper-
pressure punch, 2 – upper slab, 3 – steel chock, 4 –
lower slab, 5 – lower pressure punch, 6 – polymer
chock
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The bolt in this case was represented by two
steel punches (1) and (5), with which the pressure
from the nut and bolt head was introduced. The
diameter of the punches was 46 mm and
corresponded to the area of pressure of the M30 nut.
3 Computational Models
The computations were conducted for the geometry
of the components shown in Figure 1, Figure 2 and
Figure 3, respectively. Based on the work, [10], the
EPY resin compound behaves as a linear material.
The constants of the materials involved in the
models, namely Young's modulus E and Poisson's
ratio
, are summed up in Table 1.
Table 1. Foundation chock material characteristics
Material
E, GPa
EPY
7.5
0.376
Steel
210
0.3
Due to the plane of symmetry present in the
segment of the multi-bolted foundation connection
under consideration, only half of the connection was
included in the computations (Figure 4).
Fig. 4: Computational model of the multi-bolted
foundation connection with the steel chock
The discrete connection models formed in
Midas NFX 2023 R1, [20], are presented for all the
seating methods assumed in Figure 5, Figure 6 and
Figure 7. In the models, between the steel
components, a 'rough' contact joint model was used.
At the same time, a 'welded' contact joint model was
used between the steel joint components and the
polymer chock.
Fig. 5: FEM-S model of the foundation connection
Fig. 6: FEM-P model of the foundation connection
Fig. 7: FEM-PS model of the foundation connection
The following parameters were assumed for the
'rough' contact joint model:
• scaling factor of normal stiffness – 10,
• scaling factor of tangential stiffness – 1,
• static friction coefficient – 0.6.
The 'welded' contact elements used between the
steel joined components and the polymer chock
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prevented the components from moving relative to
each other in any direction, in line with the real
realizationof the multi-bolted foundation
connection.
The models were restrained at nodes on the
back side of the lower pressure punch in the bolt
axis direction and then subjected to normal forces at
nodes on the top surface of the upper-pressure
punch. The models also introduced boundary
conditions due to the symmetry of the connections.
By applying the aforementioned conditions, the
joined components in the multi-bolted foundation
connection models were in compression,
conforming to the real operation of this type of
connections.
The computations were carried out with a non-
linear solver in ten load steps associated with an
incremental preload of the connection from 0 to 200
kN.
4 Results of Computations
Example results of computations for the assumed
FEM-based models in terms of displacements in the
Z0X plane induced by a preload of 200 kN are
illustrated in Figure 8. Displacement values are shown
on the diagrams in mm.
To benchmark the results of the computations,
an appropriate comparison of these results achieved
for the adopted models of the tested connection was
made (Figure 9).
a)
b)
c)
Fig. 8: Displacements in the Z0X plane of the connection model under consideration induced by a force of 200
kN for: a) FEM-S model, b) FEM-P model, c) FEM-PS model
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Fig. 9: Characterization of the stiffness of
components joined in the multi-bolted foundation
connection
Subsequently, the displacements of the joined
components in the multi-bolted foundation
connection
H , representing the maximal value of
the preload , were identified.The last quantity
assumed for the quantitative comparison of the
computational models was the stiffness of the
connected components k, defined in the form:
𝑘 = 𝐹
𝛥𝐻 (1)
The values of the joined components' stiffness
achieved for the assumed multi-bolted foundation
connection models are listed in Table 2.
Table 2. Values of stiffness of joined components
for individual models
Model
k, kN/m
FEM-S
3.51
FEM-P
1.65
FEM-PS
2.65
The obtainedresults of computations lead to the
conclusion that with the use of PSCs the following
can be achieved:
• considerable increase in the stiffness of MBFCs
in comparison with connections with PCs,
• obtaining MBFCs with a stiffness comparable to
that of connections with SCs.
It should also be noted that observations of the
stresses present in the FEM-P and FEM-PS models
(not included in this article) show that, in the case of
the EPY resin compound, the stresses did not
overcome the compressive strength for this material.
5 Findings and Further Research
This article analyses MBFCs performed in 3
methods. It was demonstrated that MBFCs with
PSCs can offer characteristics of stiffness
comparable to MBFCs with SCs. Meanwhile, these
connections have the benefits inherent in
connections with PCs, the most important of which
are the unnecessary precision machining and the
close adhesion of the chock to the rough surfaces of
the machine and foundation components over the
entire nominal area of their contact.
The research presented in this article was
continued to investigate the influence of the
polymer layer thickness in PSCs on the stiffness
characteristics of the joined components in MBFCs
performed using such chocks, [].
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Contribution of Individual Authors to the
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The author contributed to the present research, at all
stages from the formulation of the problem to the
final findings and solution.
Sources of Funding for Research Presented in
a Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
Conflict of Interest
The author has no conflicts of interest to declare.
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