Modification of a metal structure due to change of use

Modificación de una estructura metálica por cambio de uso
Modificação de estrutura metálica para troca de uso

J. L. Gómez^1,2, K. Klein^1,2, G. Montiel²

¹ Facultad de Arquitectura Urbanismo y Diseño, Universidad Nacional de Córdoba, Córdoba, Argentina.

² Alconpat Argentina, Córdoba, Argentina.

*Contact author: ccp.cons316@gmail.com

Received: 05/11/2023
Revised: 16/12/2023
Accepted: 27/12/2023
Published: 01/01/2024

Abstract
The purpose of this work is to discuss the modifications made to a metal structure built in 1930, made up of triangular lattice beams supported on 60 cm thick walls and 14 interior metal columns to cover an area of 875 m² that housed the activities of the central market in the city of Deán Funes. In the 1980s the municipal management proposed its recovery for new sports uses, presenting the structural challenge of eliminating intermediate supports. The project and construction date from that time, and for this reason it is discussed the validity of the concepts and solutions adopted, as well as the importance of a maintenance plan to guarantee the degree of safety of the work.

Keywords: structural design; steel; patrimony recovery.

1. INTRODUCTION

Dean Funes, capital of the department Ischilín, is a city located in the north west of the province of Cordoba. Its origins match with the expansión of the railway back in 1875. During the first years of the twentieth century, its most significant constructions, such as the Central Market (1930), that has an Art Decó style and it is located in front of the Market Plaza (figure 1), were built. During the following years, comercial activities were moved to the outskirts of the city due to the growth of population making the building to fall on a state of abandonment. In 1982, under the government of José Naveira Ferrandes, the building is decided to be restored and a new space for sports to be placed instead. Below, the structural proyect that made posible this new use, which was designed and built back then, and at present continues to be used with that purpose, will be developed.

Figure 1. Ex Central Market of Deán Funes.

2. ORIGINAL STRUCTURAL IDEA

The original structural idea of the Market covered a surface of 875 m² which includes 26,05 m width x 33,50 m lenght. The plane on top consisted of a series of three triangular metallic lattice beams with a 8,7 m span, which made 7 axis separated by 4,19 m. A series of steel belts that made the three-section, sheet, pitched roof were standing over the unión of the angles with a distance of 2,15 m and 2,200 m. The main beams rested on14 metallic columns and on its perimeter over a 60 cm width stone wall (figure 2 and figure 3)

Figure 2. Original Municipal Drawing

Figure 3. Original axionometric of the structure.

3. NEW STRUCTURAL IDEA

In order to have only one interior space free of bases, the new structure was proyected from one plain lattice beam of 1,80 m height, connecting the already existing ones, strengthening bars and adding new elements that allow the filling up of the 26,1 m of span.

To make the design of the new main beam it was necessary to build a new upper cord, which connected the metallic profiles of the existing bridgings, and two new posts matching the previous support that withstands the compression stresses and allows the lenght of the new cord’s bending to be reduced (figure 4).

Figura 4. Axonometric of the structural idea.

Equally, upper brace beams with two profiles UPN 80 were set in order to reinforce that concept and to avoid the lateral bending perpendicularly to the beam’s design (figure 5).

Figure 5. New exterior structure roof’s plan

On the other hand, both the inferior cord and some requested existing diagonals were reinforced in order to withstand the internal stresses of traction and compression from the evaluation of the new structural behaviour,

4. METHOD OF CALCULATION

Next, it will be presented the method of calculation based on the regulations and available tools at that time, but which have validity at present.

4.1 Analysis of loads

At first, an analysis per square meter was conducted to determin the magnitude of the punctual actions over the new lattice beam’s unión of its angles (figure 6).

Figure 6. Lattice beam with numbered bars, (nudos), and loads.

4.1.1 Analysis of loads per square meters

• Corrugated sheet ------------------------------------- 10 kg/m²

• Wooden beams --------------------------------------- 6 kg/m²

• Lattice beam’s dead load--------------------------- 22 kg/m²

• Superimposed usage -------------------------------- 25 kg/m²

• TOTAL ----------------------------------------------- 63 kg/m²

4.1.2 Analysis of loads over girder’s union of its angles

• Strut loads ----------63 kg/m² x area of influence (4,19 x 2,2 m x 2) = 1162 kg

4.2 Determination of requests

To calculate the normal stresses, a PPlan program from the Taller de Investigación de Diseño Estructural (TIDE) of the Faculty of Architecture of the National University of Cordoba was used. At that momento, the coordenates that defined the beam’s geometry and the actions over itself were intriduced. As a result, the values of stresses in each unión of its angles which are summarized in the following table 1 were printed out.

Table 1. Requests and reactions.

4.3 Verification of general deformations

Considering the dimensions and analysis of the requests, the upper cord was premeasured with two profiles UPN 120 making a drawer-like section with an área of 27 cm², and the inferior cord was premeasured with two matched UNP 100 profiles with an area of 22 cm² (figure 7).

Figure 7. Compound section of the lattice beam.

From the analysis of the parameters that intervene in the determination of the maximum arrow, there was established the following data:

-Moment of inertia of the group J =392.769 cm⁴

^- Load “q” 63 kg/m² x 4,19 m = 260 kg/m

4.3.1 Calculation of the maximum arrow

4.3.2 Calculation of the admisible arrow

4.3.3 Comparison maximum arrow< admissible arrow

4.4 Sectional verification and proposals of the structure’s reinforces

After the control of deformations, a sectional verification was conducted. First, regarding the new structural elements of the upper cord and the uprights. Second, regarding the resistance of the existing elements subdued to new efforts such as the inferior cord and the diagonals (figure 8).

Figure 8. Section of the lattice girder.

4.4.1 Upper Cord

As previously stated, the upper cord was carried out by the drawer-like section made of two UPN 120. The necessary data to verify the resistance is shown in table 2.

Tabla 2. Datos del cordón superior

Calculation of the minimun ratio turn

Calculation of the slenderness

Rate of the bending for steel F24

$ɷ=$ 2,07

Calculation of the strain of work

4.4.2 Studs

The studs were defined by a drawer-like section as well, but made by two UPN 50. The necessary data to verify the resistance is shown in table 3.

Tabla 3. Uprights Data

Calculation of the minimun ratio turn

Calculation of the slenderness

Rate of the bending for steel F24

$ɷ=$ 2,05