Characteristics of Wooden Architecture: Differences from Reinforced Concrete and Steel Structures

Introduction

The Rise of Wooden Architecture

In recent years, I have increasingly been asked to design wooden structures for projects other than residential homes. There are many cases where buildings that would previously have been designed using reinforced concrete or steel, such as public offices or corporate welfare buildings (employee break rooms), are now being intentionally built with wood.
Therefore, to organize my own thoughts, I would like to write about the structural differences between wooden buildings and other types of construction.
(Here, I will write from the perspective of structural strength, such as resistance to earthquakes. Regarding design and environmental performance, there are various other characteristics separate from what is written here.)

What is the Biggest Characteristic of Wooden Architecture?

While wooden construction has characteristics such as high variability in strength due to being a natural material and the difficulty of creating large-span structures, I believe thebiggest difference is that the columns and beams are pin-connected,
.

Pin Connections and Rigid Connections

The methods for connecting structural members are broadly divided into two types: pin connections and rigid connections.
Explaining these two...

What is a Pin Connection?

A pin connection refers to a method where, as shown in the figure below, wooden columns and beams are joined with hardware or bolts, but theoretically, they are only joined at a point, allowing for rotation. Wooden construction is basically pin-connected.

What is a Rigid Connection?

Unlike a pin connection, a method that is joined firmly so that it does not rotate is called a "rigid connection." General steel and reinforced concrete structures often use this type of connection. (There are also steel structures that use pin connections.)

There are ways to make wooden structures rigid-connected, but there are many constraints, such as the need for large columns and beams or the use of special hardware.
In the first place, due to the material properties of wood, it is not possible to firmly bond the entire joint surface with methods like welding, making it unsuitable for rigid connections.

Resisting Seismic Force

Next, I will write about how each structure resists seismic force.
If gravity is a force acting vertically toward the ground, seismic force is a force acting horizontally from the side.

In the Case of Reinforced Concrete and Steel Structures

When seismic force (force from the side) is applied to the framework of a reinforced concrete or steel structure that uses rigid connections, the entire framework withstands the force and resists the seismic force.
This is the main structure for reinforced concrete and steel buildings, known as a rigid-frame structure.
(There are also reinforced concrete and steel structures that are not rigid-frame structures.)

In the Case of Wooden Structures

However, in the same way, when seismic force is applied to a wooden frame, because the wooden structure uses pin joints, it will collapse as shown in the figure below.

So, what should be done? In wooden structures, braces or plywood are used to resist horizontal forces.

Therefore, where to place these earthquake-resistant walls, such as braces or plywood, becomes important. Since it also greatly affects the design, coordination with the architectural designer is necessary from the initial stage.

Actual requests

However, in reality, designers or architectural designers sometimes ask, 'Can't you make a connecting corridor with just columns and beams to keep it clean?' which gives me a headache...
I understand what they want to say, so I want to meet their requests as much as possible. But I cannot build a dangerous building.
As shown in the title photo, attaching diagonal members called 'braces' (hozue) to the upper part is a common method for connecting corridors and gazebos.
But if they say that the braces are also different in terms of design... Should I use special hardware to make the column-beam joints rigid? Or should I partially insert steel braces? There are projects I am still struggling with.

I wish I had a few 'this is it!' solutions in my drawer. I am currently looking for similar designs.
If there are any buildings that could serve as a reference, please let me know.

I have various thoughts about wooden structures, so I plan to write about them on my blog as part of my own study.
The themes will include hardware, joining methods, seismic retrofitting, and so on.
I would appreciate it if you could give me your various opinions.