# The Behaviour of Load-Carrying Members from Cordwood

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

_{2}. Cordwood is used in structural members subjected to compression, such as walls and columns. Its compressive behaviour was investigated in some studies [15]. The methods for laboratory tests enable the determination of cordwood compressive strength, so the obtained results are also presented [16]. However, the design methods for compressed cordwood wall structures are not shown in detail.

## 2. Materials and Methods

#### 2.1. Analytical Method for the Design of Cordwood

_{d}is determined as a relation of the characteristic compressive strength ${\sigma}_{\mathrm{c},\mathrm{m}}$ and the safety factor Υ

_{M}, which is equal to 2.7 [23].

#### 2.2. Analytical Method for the Design of Cordwood in Case of Fire Action

_{g}is the gas temperature; α

_{c}is the heat transfer coefficient by convection; ε

_{m}is the surface emissivity; σ is the Stefan–Boltzmann constant.

#### 2.3. Developing Comparison Criteria for Cordwood

_{1(k,j)}. The factor can be determined by Equation (8). Its essence is to find factor k

_{1(k,j)}as the ratio of the total strength of the masonry to the strength of the wood used or the strength of the mortar concerned. This factor establishes the proportion of the materials used for the maximum compressive strength in the constructed parapet wall.

_{c,m}is the compressive strength of cordwood; f

_{c,k}is the characteristic compressive strength of timber perpendicular to the grain (f

_{c,90,k}); f

_{c,j}is the characteristic compressive strength of the mortar.

_{2}, which can be determined by Equation (9).

_{m}, V

_{j}and V

_{k}are volumes of cordwood, mortar and wood, correspondingly.

#### 2.4. Description of Laboratory Experiment

#### 2.5. FEM Modelling of Cordwood Specimens

## 3. Results

#### 3.1. The Numerical Realisation of the Developed Analytical Method for the Design of Cordwood

_{ed}, is equal to 226.10 kN.

_{R,d}was determined by Equation (3) for the case where the designed compressive strength of cordwood is equal to 0.815 MPa, and factor ɸ is equal to 0.75. The designed load-carrying capacity of axially loaded cordwood wall N

_{R,d}was 244.50 kN. The relation of N

_{ed}to N

_{R,d}is equal to 0.93 and means that the cordwood wall fragment’s load-carrying capacity is provided.

#### 3.2. The Numerical Realisation of Developed Analytical Method for the Design of Cordwood in Case of Fire Action

_{fi}= 0.6 for timber structures and η

_{fi}= 0.65 for masonry structures [24,28,29]. For the case study, a more conservative value of η

_{fi}= 0.65 will be used.

_{fi,d}, is equal to 147.0 kN. The safety factor in fire: γ

_{M,fi}= 1 (according to Ref [29]); the design strength in case of fire: f

_{d}= 2.2 MPa.

_{R,Fi,d}= 391.1 kN. R240 is ensured.

_{R,Fi,d}= 250.8 kN. R180 is ensured.

#### 3.3. Results of the Laboratory Experiment

_{1(k,j)}and k

_{2}were determined based on the laboratory experiment results to compare the effectiveness of the considered cordwood specimens. A comparison of the overall strength of cordwood against the compressive strength of wood billets shows that woods with the most effective mechanical properties are used for cement mortar cordwood specimens k

_{1(k)}= 0.902, lime mortar k

_{1(k)}= 0.517 and k

_{1(k)}= 0.170 for clay cordwood samples, respectively. Looking at the k

_{1(k)}values obtained, which determine the overall strength of the masonry in relation to the compressive strength of the mortar, it can be concluded that the most effective mechanical properties of the mortar are used for the clay and lime mortar cordwood specimens, respectively (0.220 and 0.192). The high strength of cement mortar is practically not used k

_{1(j)}= 0.063. The results obtained with the highest specific strength were found for lime mortar k

_{2}= 0.069, followed by clay samples 0.046, and the lowest specific strength is expected from cement cordwood samples—0.030. It can be concluded that a more efficient use of material properties occurs for the cordwood specimens produced with the lime mortar. The results show that the high strength of the mortar used does not significantly affect the overall strength of cordwood.

#### 3.4. Results of FEM Modelling

## 4. Conclusions

- The most rational and economical cordwood solution involves using a low- or medium-high-strength mortar (up to 10 MPa). The use of higher strength mortar does not significantly increase the strength of cordwood. It was proven experimentally that the use of mortars with compressive strengths of 36.76, 7.12 and 1.94 MPa for producing cordwood specimens enables obtaining a compression strength of cordwood of 2.14, 1.22 and 0.43 MPa, respectively. The increase in the wood billets’ strength class did not significantly influence the compressive strength of cordwood. Therefore, increasing the strength class of wood billets from C16 to C30 increased the compressive strength of cordwood to 21% only when the lime mortar with a compressive strength of 7.12 MPa was used. By using a cordwood wall with a thickness of 40 cm, which corresponds to the most commonly used cordwood wall thickness, it is possible to obtain load-bearing walls for two-storey buildings that provide very high fire resistance—R180, in the case of double-sided fire resistance.

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**(

**a**) Pedestrian bridge with wood logs in Rodini Park, Rhodes; (

**b**) cordwood specimens considered in the current study.

**Figure 4.**Laboratory specimens with the different types of mortars: (

**a**,

**b**) lime mortar; (

**c**) clay; (

**d**) cement mortar.

**Figure 7.**Applied boundary conditions (

**a**) and development of contact surfaces between the wood and mortar (

**b**).

**Figure 9.**Laboratory tests for cordwood components: (

**a**) testing of wood billets; (

**b**) testing of clay and mortar cubes.

**Figure 10.**Result of cordwood specimens testing: (

**a**) placement of the cordwood specimen in the testing machine; (

**b**) mean compressive strength of cordwood as a function of the maximum compressive strength of the used mortar.

**Figure 11.**The behaviour of the cordwood specimen C-1, obtained by the FEM model: (

**a**) development of the crack in the course of loading; (

**b**) total displacements of cordwood specimen under the action of maximum compression force.

**Figure 12.**The behaviour of the cordwood specimen C-1, obtained by the FEM model: (

**a**) displacements of cordwood specimen under the action of maximum compression force in the direction of the Y-axis; (

**b**) distribution of resulting normal stresses in the cordwood specimen under the applied maximum axial force; (

**c**) distribution of resulting normal stresses in the cordwood specimen in the direction of Y-axis under the applied maximum axial force.

**Figure 13.**Influence of the wood strength classes on the behaviour of cordwood: (

**a**) force/deformation curves for the cordwood specimen differed with the wood strength classes; (

**b**) compressive strength of cordwood as a function of the strength classes of the wood.

**Figure 14.**Influence of the mortar compressive strength on the behaviour of cordwood: (

**a**) force/deformation curves for the cordwood specimen differed with the mortar compressive strength; (

**b**) compressive strength of cordwood as a function of the compressive strength of mortar.

Time t, min | Charring Depth d_{char,0}, mm | Depth of 300 °C Isotherms in Mortar, mm | Reduction in Wall Cross-Section, mm |
---|---|---|---|

30 | 19.5 | 29 | 36 |

60 | 39.0 | 51 | 57 |

90 | 58.5 | 66 | 73 |

120 | 78 | 78 | 85 |

180 | 117 | 102 | 124 |

240 | 156 | 120 | 163 |

**Table 2.**Depth of 300 °C isotherms for timber and mortar wall in case of double-sided fire for walls with thicknesses b equal to 200 mm, 300 mm and 400 mm and more.

Time t, min | Charring Depth d_{char,0} | Depth of 300 °C Isotherms in Mortar, mm/Reduction in Wall Cross-Section, mm | ||
---|---|---|---|---|

b = 200 mm | b = 300 mm | b ≥ 400 mm wall | ||

30 | 19.5 | 29/72 | 29/72 | 29/72 |

60 | 39.0 | 51/116 | 51/116 | 51/116 |

90 | 58.5 | 69/152 | 66/146 | 66/146 |

120 | 78 | -/- | 81/176 | 78/170 |

180 | 117 | -/- | 116/248 | 105/248 |

240 | 156 | -/- | -/- | 123/326 |

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**MDPI and ACS Style**

Brics, A.; Serdjuks, D.; Gravit, M.; Buka-Vaivade, K.; Goremikins, V.; Vatin, N.I.; Podkoritovs, A.
The Behaviour of Load-Carrying Members from Cordwood. *Buildings* **2022**, *12*, 1702.
https://doi.org/10.3390/buildings12101702

**AMA Style**

Brics A, Serdjuks D, Gravit M, Buka-Vaivade K, Goremikins V, Vatin NI, Podkoritovs A.
The Behaviour of Load-Carrying Members from Cordwood. *Buildings*. 2022; 12(10):1702.
https://doi.org/10.3390/buildings12101702

**Chicago/Turabian Style**

Brics, Arvis, Dmitrijs Serdjuks, Marina Gravit, Karina Buka-Vaivade, Vadims Goremikins, Nikolai Ivanovich Vatin, and Andrejs Podkoritovs.
2022. "The Behaviour of Load-Carrying Members from Cordwood" *Buildings* 12, no. 10: 1702.
https://doi.org/10.3390/buildings12101702