Arch

An arch is a curved shape.

It can hold up heavy things. It can also just look pretty. Arches help us build strong walls. They help us make big doors.

Arches can be many shapes. Some are round. Some are pointed.

An arch can be made of stone. It can also be made of brick or steel.

They are very useful tools for builders.

An arch is a curved structure that spans an open space.

Arches can hold up heavy weight. They can also just be for decoration. Ancient Romans made structural arches very popular. They used them to build strong things.

A true arch works through compression. This means the parts are pressed together.

Most arches use wedge-shaped blocks. We call these blocks voussoirs. The top block is the keystone. It holds everything in place. The bottom of the arch is called the intrados. The top surface is the extrados.

Arches have many different shapes. Some are round, like a semicircle. Others are pointed.

Some look like a horseshoe.

Builders use different materials for arches. They use stone, brick, or concrete. They also use steel. Steel is very strong. It allows for long, straight beams instead of arches. But arches are still great for carrying weight. They can span large gaps using small pieces of stone.

An arch is a curved structure that spans an open space. It can be used to hold up heavy weight or just to look pretty.

While people used arches for decoration long ago, the Ancient Romans made them very popular for building. They used arches to support heavy loads in their structures. This is different from a trabeated system. In that system, builders use simple posts and beams. Arches allow builders to span larger gaps with the same amount of material. They also let people use smaller, easier pieces to build big things.

A true arch works through a way called arch action.

This happens because the weight from above is turned into pressure. This pressure pushes the parts of the arch together. This is called compression. Most masonry arches use wedge-shaped blocks called voussoirs. The very top block is the keystone. It is the most important piece for holding the arch together. The bottom surface of the arch is the intrados. The top surface is called the extrados. The weight pushes down, but the ends of the arch push back against the walls.

In 1676, a man named Robert Hooke noticed something interesting about arches. He saw a link between hanging chains and rigid arches. He said that a rigid arch stands like an upside-down hanging chain.

This shape is called a funicular shape. The exact curve of an ideal arch depends on how the weight is spread out. In the past, builders assumed stone could handle huge amounts of pressure. However, stone is not good at being pulled apart. This is why the pieces must stay pressed tightly together to keep the arch stable.

There are many different types of arches. Some are rounded, like the semicircular arches used by the Romans.

Others are pointed, which you might see in Gothic buildings. You can also find horseshoe arches or even basket-handle arches. Arches can be arranged in a long row called an arcade. The Romans were very good at building these. Some arches are even built to be decorative, like the blind arches used in Islamic architecture. These arches do not actually hold up a roof but look beautiful on a wall.

Today, we use many different materials for arches. Builders use stone, brick, concrete, and even steel. In the middle of the 19th century, things changed with the invention of wrought iron and steel. These new materials have high tensile strength. This means they can be pulled without breaking. Because of this, builders can use long, straight beams instead of arches for many jobs. However, arches are still used for many special things. You can see huge, beautiful examples like the Gateway Arch in St. Louis.

An arch is a curved vertical structure that spans an open space. These structures serve two main purposes in architecture. They can support heavy loads from above, or they can be used purely for decoration. While decorative arches date back to the 4th millennium BC, structural load-bearing arches became widely popular after the Ancient Romans adopted them in the 4th century BC.

Arches work differently than the trabeated system. In a trabeated system, builders use posts and beams, much like in ancient Greece, China, or Japan. An arch offers several advantages over a simple lintel or beam. With the same amount of material, an arch can span a larger distance. It can also carry more weight and is made of smaller, more manageable pieces. This makes masonry construction much more efficient.

A true arch is a load-bearing structure held together by compression. Compression is a force that pushes materials together. To understand the parts, we look at the individual blocks called voussoirs. These are wedge-shaped construction blocks. The very top block is called the keystone. The area around the keystone is known as the crown. The underside of the arch is called the intrados, or the soffit. The external surface is called the extrados. At the base, the arch rests on a block called an impost. The vertical distance from the springing level to the crown is called the rise.

The way an arch handles weight is called arch action.

When a vertical load is placed on the arch, the structure resolves that weight into both vertical and horizontal reactions at the ends. This creates a bending moment. However, the inward horizontal reaction from the abutments provides a counterbalancing force. This means the bending moment in any segment of the arch is much smaller than it would be in a beam. In a beam, the top is in compression but the bottom is in tension. In a true masonry arch, the elements are mostly subject to compression. Because masonry has very low tensile strength, the pieces must stay pressed together to prevent collapse.

In 1676, Robert Hooke discovered a fundamental symmetry in how these shapes work. He noted that a rigid arch stands like an inverted hanging chain. This relationship is called a funicular shape. The specific curve of an ideal, compression-only arch depends on how the load is distributed. Builders often use a pressure polygon to ensure stability. As long as this curve stays within the confines of the voussoirs, the construction remains stable.

Arches can be classified in many ways, including their shape, material, or structure. They can be rounded, such as the semicircular arches used by the Romans. They can also be pointed, which is a characteristic of Gothic architecture. Other shapes include the horseshoe arch, often seen in Islamic architecture, and the basket-handle arch.

You can also find segmental arches, which are less than a semicircle. These were used in Ancient Egypt as early as 2100 BC.

Architects often arrange arches in specific patterns. A sequence of arches can form an arcade. The Romans perfected this, using them in massive structures like the Pont du Gard. Some arches are "blind arches," meaning the opening is filled in for decoration. Others are "relieving arches," which redirect weight to stronger points in a building. There are even "strainer arches," which were sometimes built as an afterthought to prevent supports from imploding due to miscalculations.

The role of the arch changed in the mid-19th century with the introduction of wrought iron and steel. These materials have high tensile strength, meaning they can be pulled without breaking. This allowed for long lintels and beams that did not require an arch shape. However, arches remain iconic and functional. Large-scale examples, such as the Gateway Arch in St. Louis, continue to demonstrate the power of this geometry.